The AWD Tacoma Mod - Swapping in the 3rd Gen 4Runner T-case

OBJECTIVE:

Adding All-Wheel-Drive as an option to the 1st gen Tacoma by utilizing the 3rd Gen 4Runner Multimode Transfer Case.​

MOTIVATION:

So why would you want AWD on a Tacoma? Well, there are plenty of on-road conditions where AWD might have an advantage. Roads that are a mix of slippery conditions and high traction. For example, unplowed side streets followed by cleared main road that is high traction, highways that are primarily dry followed by snowy/icy patches that haven't melted yet, or winding mountain passes with mixed dry and slippery conditions (typically where the shade of the terrain prevents the sun from melting the snow). These conditions are prevalent where I live and in the nearby mountains. You can set the truck in AWD and drive normally in these conditions.


An example of where AWD is a great choice. Notice perfectly dry, high traction paved road followed by icy patches and a curve approaching. The curve had patches of ice and high traction.

Note: Perhaps you think, "Gee Whiz, this is a lot of work for a small benefit in specific circumstances." You're right; you always are. To each their own. I irrationally have fun figuring this stuff out, working on the truck, troubleshooting, and even writing about it, so I'm not too worried about its cost vs. time vs benefit analysis. It’s a mark of a true engineer to spend absurd amounts of time and energy figuring out how to correct a minor inconvenience or save a few seconds.
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VIDEO:

If you'd rather be entertained by watching me do the work over a span of ~20 minutes, check out my video:

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BACKGROUND:

It is essential to understand the difference between 4-Wheel Drive (aka 4WD, "4WD Locked", "part-time 4WD") vs. All Wheel Drive (aka AWD, "4WD unlocked", "full-time 4WD"). With this understanding, you will understand the potential benefits of the mod. You can skip this if you know already. Here is a quick summary to review the concept:

Both AWD and 4WD systems transfer power to all four wheels. When a traditional front-steered vehicle is in a tight turn, all wheels follow different paths during the turn, thereby turning at different rates. For example, the inside tires spin slower than the outside tires. This is why all powered axles have differentials between the wheels, allowing both wheels on that axle to rotate at different rates in turns, even while applying power. The rear axle's wheels tend to cut more to the inside of the arch as compared to the front axle wheels, as the rear wheels "follow" the vehicle's orientation. This means that collectively, the front axle turns faster than the rear axle.

The Transfer Case in the Tacoma with 4WD engaged does not allow the front and rear axles to spin at different rates in turns. The front and rear driveshaft are forced to spin at the same rate. Essentially, the tires want to spin at a specific rate in a turn, but the drivetrain forces them to rotate at a different rate than "natural," typically causing the tire to break traction to release the tension built up. The system is sometimes called "part-time 4WD" since you should only use it "as needed" and on a relatively low traction surface. You have likely felt a binding or stuttering when trying to make a tight turn with 4WD on. Hopefully, you were on the trail or in slippery conditions, where the traction is generally much lower, and the binding can release itself without causing damage by slipping a tire (typically the one with the least traction). However, if you were to try this on dry pavement, a tremendous amount of torque would be placed on all the drivetrain components, which is terrible for the system in general.

AWD, by contrast, has a center differential between the front and rear driveshafts. This differential allows the front and rear axles to spin at different rates as conditions dictate. AWD can be used on high traction surfaces, as no binding occurs in the system in tight turns. Hence "full-time 4WD" can be used on the trail; high traction and slippery conditions don't matter. However, A disadvantage of the system is that if one wheel is in the air on the trail, all power goes to the wheel that spins the easiest, and you can get stuck. But that’s what part-time 4WD, front lockers, and rear lockers are for

If you need more info, check out a couple of great videos below:



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MOD APPLICATIONS:

I'm doing this mod on a 4WD TRD Off-Road Tacoma. This Tacoma came with the "4WD Shift Button" on the side of the T-Case Shift lever. 4Runners with the Multimode T-Case also use the same button on the side of the shift lever. If you plan to use this as a guide, I cannot speak for the Tacomas that have to fully manual J-shift T-case. You will likely have to do much more extensive wiring than a Tacoma with the push button T-case actuation.

However, the TW community may expand this guide for other Tacomas with manuals and J-shifters.​

MOD OVERVIEW:

I will adapt the 3rd Gen 4Runner Multimode T-Case (MMTC) into the Tacoma. This transfer case includes a selectable locking center differential. In addition to the features already present on the Tacoma T-case (TTC), the MMTC allows for AWD mode via an unlocked center diff. Essentially, when you press the button for 4WD, the MMTC shifts into 4WD with the center diff unlocked (aka AWD). By pushing a button, the MMTC locks the center diff, and you have true 4WD. From there, the MMTC can also have a high/low range via the T-case shift lever.

The mod can be divided into three phases:

1. Mechanical (in this post) - Swapping out the TTC to the MMTC
2. Electrical/Controls - Splicing in the MMTC Harness, Adding Pins to the MMTC Controller, Creating a few new circuits to support the controller
3. Display - Creating a display to indicate when in AWD and 4WD
4. Testing - Making sure it works as intended

Note: I'm creating a lot of extra work for myself by trying to adapt the 4Runner cluster display into its gauge. A much simpler solution would use LED indicator lights with labels, markers, or whatever.
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PARTS & TOOLS:

Parts from Donor 4Runner (A/T w/ Push Button 4WD) - See this link ( ) for a guide of all 4Runenr T-cases.

Another helpful parts sourcing tool for local salvage yards: https://www.car-part.com/

I've included approximate prices I paid in January 2023 at a local salvage yard for reference.

1. Multimode Transfer Case with Harness Section ($250)
   
   
   
2. Transfer Case Control Module ($60) - referred to as 4WD Control Computer P/N 89533-35170
   
   Note: I asked for the controller connector pigtail as a reference, but it is unnecessary. Also in the picture is the OEM Center Diff Lock Switch
   
   
3. Front Driveshaft ($40) - Ensure the driveshaft came off a vehicle with the MMTC, or else it will not be long enough. T4R Fr Driveshaft (top) vs. Tacoma Front Driveshaft (bottom)
   
   
   
4. Single Cab Application only (~$70)- The T4R Rear Driveshaft should be the correct length
   
   
5. OPTIONAL - OEM Center Diff Lock Button with connector pigtail ($15) (see controller pic above)
   
   
6. OPTIONAL - OEM Instrument Cluster ($100) (for the 4WD System Indicator)
   
   Just after this pictogram-type indicator in the T4R Cluster

Electrical Parts -

1. SPST Momentary On Switch
   • Option 1: Use T4R OEM Center Diff Switch
   • Option 2: Find your own switch that works
2. Some indicator lights to know when you're in AWD vs. 4WD (if you chose not to use the one in the 4Runner Cluster).
   • Easy Option: Use any indicator lights or displays you like and mount them wherever. An example below:
     
   • Hard Option: Adapt the OEM
3. 18-22AWG the more colors, the better. (TXL (thin insulation), GXL (medium insulation), or SXL (thick insulation) if you wanna get fancy with your wiring game).
4. Wire protection of some sort (split loom flexible conduit or expandable braided sleeve). Protect your wiring, folks; the automotive environment is especially harsh.
5. Electrical Tape
6. Adhesive Lined Shrink Tubing
7. Electrical Butt Splice Connectors, I prefer the closed barrel types, but use whatever you like.
8. Electrical Terminal Contacts - TE Connectivity 175265-1 (for controller connector)
9. I'll detail some more parts I used in the electrical section as they are not strictly required.

Tools

• The usual automotive tools (metric sockets, ratchets, extensions, pliers, etc.)
• Transmission Jack (unless you're going to hulk it in). Or do what I did, a piece of plywood attached to a floor jack. Sketchy, for sure; I would get the trans jack next time.
• Quality Electrical Contact Crimpers
• Wire Strippers
• Multimeter for testing, troubleshooting
• Heat Gun (or torch used carefully if you're a savage)

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MECHANICAL PHASE:

The 3rd gen 4Runner and the 1st gen Tacoma are remarkably similar in many ways, as both are built with the same engine, transmissions, and platform. The MMTC bolts up to the transmission extension housing without an adapter (can only speak for the A/T). I've noted some of the key differences below when it comes to the swap to look out for.

I won't go into great details on how to do the physical swap, as many great resources exist for reference (video of removal linked below). You can just enjoy a few pics of the key moments in the process.

Driveshafts

The MMTC is significantly longer than the TTC. The front and rear output flange from the MMTC will be approximately 3-1/8" further back than the TTC. This means you will need different driveshafts, both front and rear. Luckily, the 4Runner front driveshaft from the donor vehicle will work perfectly. Swap out the Tacoma's front Driveshaft with the 4Runner's, and you are good to go. For reference, the distance I measured between the front differential input flange to the T-case front output flange is 30-1/8".


A brief comparison of the MMTC (left) to the extra dirty TTC (right)

For Extra Cab and Double Cab Tacomas, the Rear Driveshaft will need to be shortened by 3-1/8". The front portion of the rear driveshaft (between the T-case and the carrier bearing) makes the most sense to shorten, so you don't have to relocate your carrier-bearing mounting point. After shortening, the shaft from flange to flange was almost exactly 27" in length.

IMO, modifying the driveshaft is worthwhile to have done at a driveshaft shop. They can shorten and rebalance the shaft to your specs. In my area, the shortening and rebalancing cost $300 (Feb 2023). You could attempt to cut and reweld your driveshaft, but considering how fast this thing spins and the loads it is under, it is critical that the shaft is absolutely straight, balanced, and strong.


For regular cab Tacomas, consider yourself lucky. Use the rear driveshaft from the same 4Runner, as it is already the correct length.
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Vehicle Speed Sensor

Unlike the Tacoma, The 4Runner does not have a vehicle speed sensor near the T-Case output flange. On the MMTC, there is a hole to accept the sensor, but it has a large plug installed. Remove the plug and install the sensor in its place.

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Highlight Reel

Driveshafts disconnected

Shifter Assembly Out. The previous owner did a hack job on this; you'll see it later.

Transfer Case Shift Lever Out

Extension Housing to T-case Bolts coming out

TTC Coming Out

Just Barely cleared the frame.

I took the extension housing off to access the nut plate the shifter bolts thread into for repair. You should not usually need to do this to complete the swap. I refreshed some of the components while I had it apart.

Nice of the previous owner to leave half of these rusty shifter bolts stuck and chowder the others. My OCD won't allow this. It must be fixed.

Restored, new weld nuts, rust converted, painted.

The OEM transfer case shifter seat was utterly disintegrated into a sand-like consistency. So I cleaned it up and replaced the seat with a marlin crawler shifter seat.

MMTC Going in. After doing this the sketch way, I highly recommend a proper trans jack.

It's a huge relief to get everything lined up and that first bolt goes in.

Installing the rest of the bolts.

"New" Shortened Rear Driveshaft

Driveshaft going back on.

Don't forget to fill T-case with oil... there is a story behind why I add that "NO OIL" tag.​

ADDITIONAL RESOURSES:

While researching this, I found these to be helpful.

• https://www.tacomaworld.com/threads...-4-wheel-drive-or-automatic-to-manual.702733/
  
• https://www.tacomaworld.com/threads/transfer-case-transfer-cases-in-first-and-2nd-gen-trucks.345652/
• https://www.tacomaworld.com/threads/1st-gen-transfer-case-identifcation-for-replacement-swap.753707/
  
• 4Runner Factory Service Manual
• Tacoma Factory Service Manual

T-Case Swap/Replacement Resource

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NOTE: There is a lot to write up, and I will do it in stages. I'm also making a video about the swap, which makes the mod that much longer for me. I will release the video and complete the write-up soon. I'm very close to a test drive at the time of this post.

UPDATES:
03/7/2023 - System tested and running. Modification verified and complete!
03/13/2023 - Electrical Writeup Complete.
03/31/2023 - Video Uploaded, see above.
04/03/2023 - Display Writeup Complete

Any feedback/questions are welcome. I will edit these posts based on new developments, discover I missed something, particular questions, or helpful things you share.

 

ELECTRICAL & CONTROLS PHASE:

The bulk of the work from this swap comes from the wiring. The TCC and MMTC use different control modules due to the 4Runner having increased functionality. The MMTC controller is "plug and play"…. To a point.


Tacoma 4wd Controller Connector (right) vs. 4Runner's (left). Hint: They are the same! ... besides the color.

The existing Tacoma connector will plug in physically without modification. Noice. The existing Tacoma connector has 18 wires, 17 of which are directly compatible with the 4Runners controller, no modification needed. WHOA! Only one wire needs to be swapped from one position to another. DAYUM! So Easy. It's almost like it's too good to be true.

Below is a table of direct circuits that exist in both the T4R and the Tacoma that are compatible. Only one pin needs to be swapped, highlighted in yellow:


Table of circuits that exist on both the Tacoma and 4Runner Controller. Highlighted in yellow is one circuit that needs to be swapped in the connector.

What's Different?

Okay, did you really think that would be that easy? Before you or I get too excited, six new circuits are on the 4Runners controller, which I must adapt to make it work.

Here's an overview of the differences between the MMTC electrical and control system compared to the TTC system:

1. Both systems use a different controller mounting strategy & location - Need to adapt the T4R Controller to mount in the Tacoma's controllers position
2. 4Runners Controller is physically bigger; modification is needed to make it mount nicely.
3. MMTC is physically longer (see above post) => the Tacoma Factory harness cannot reach all connections (at least without significant strain on some connections)
4. MMTC has an additional position Sensor for detecting between AWD and 4WD.
5. MMTC has an input from the Transmission Shift Position switch
6. MMTC has an additional input from the 4WD actuator limit switch
7. The MMTC controller utilizes two outputs to display 4WD vs. AWD modes to the driver
8. The MMTC controller has an input from the center diff lock button.
9. MMTC has an output to the 4Runner ECU

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More Modification Application Notes:

The swap I'm doing needs the controller from a '01-'02 4Runner. Why you ask? The 4Runners from year 2000 and older used a vacuum-actuated A.D.D. and therefore used different controllers. So even if the 4Runner was equipped with the MMTC (the limited trim models before '01), it will not have a controller like the one in this swap. Not to say it can't be done, but probably not like this exactly.


This could be good news, however, as there is potential that Tacomas with the vacuum-actuated A.D.D. could also potentially swap an MMTC in from an older 4Runner ('96-'00) using that 4Runner's controller. More research needs to be done to confirm.
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Controller Mounting

Regarding controller mounting, the MMTC and TTC use different mounting locations and orientations. The TTC "lays flat" under the head unit behind the center stack console ( the trim peice surrounding the radio, HVAC controls, etc. The MMTC Controller is also significantly bigger than the TTC controller.



I needed to mount the MMTC Controller roughly in the same spot as the TTC Controller to simplify wiring modifications. If I don't, well, I'll have to modify the lengths of 18 separate wires in addition to the changes already needed. No thanks. Since the boxes are significantly different in size, the MMTC controller will not fit in the same space "laying down" as the TTC controller.

I started by separating the circuitry from the box to prevent damage while I bent/banged/welded the enclosure to make it work in the space. The 4Runner's metal enclosure and the circuit board are just held together with some bent-over metal tabs making disassembly a breeze.

To mount the controller, I planned to use the same bolt and weld nut used to mount the original controller. I cut part of the existing mounting tab gusset off to make it easier to bend and find the shape of the tab that will work for the space.


Bending the mounting tab and mocking up the controller mounting location.

Once happy with the mounting tab, I welded in some small gussets to make the tab more rigid. Since the module is cantilevered out horizontally, I needed an anti-rotation feature to prevent the controller from rotating down over time. I used a "pin and hole" feature to ensure it would not rotate. I was also worried about how far the controller cantilevered from the center support brackets. It's pretty "vibrate-y" when you fling it as mounted, like when you flick an antenna.



To address this, I welded some metal behind the tab it bolts into, stiffening the entire bracket. It should not vibrate too much between that and the stiff wiring harness that plugs into it opposite the bracket.


Ugly. Welded in a small piece of angle iron to stiffen this tab and reduce virbations


End result - Controller mounted

Note: I did consider cutting the tab off entirely and using a strong tape to stick it to the top of the SRS Module (aka the "airbag module," the one with the yellow harnesses going to it). Although it would probably work, I was concerned about the heat that might need to be dissipated between the modules. Mounting them with no gap could be an issue, but hard to say whether it would be for sure. That's why I ended up with this configuration.
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The New Circuits Explained:

1. 2WD-4WD Motor Limit Switch - The controller receives a signal from the 4WD actuator to know when to stop/start the actuator motor. The 4Runner has an additional limit switch because it has an additional mode compared to the Tacoma. This limit switch comes off the 6-pin actuator connector. It will need to run from the MMTC actuator to the controller. See "Splicing the MMTC Harness to the Tacoma Harness" for more details about routing.
   
   
2. Center Diff Lock Position Switch - The controller receives a signal from the shift rail position sensor to confirm that the T-case is indeed "locked." The 4Runner has an additional position sensor since, you guessed it, it has another mode it needs to confirm. See "Splicing the MMTC Harness to the Tacoma Harness" for more details about routing.
   
   
3. Center Diff Lock Switch - The 4Runner has a switch on the dash to command the center diff to lock, thereby shifting from AWD to 4WD and vice versa. The switch grounds the input when pressed, signaling the controller to switch. See "Dash Switch Mounting & Wiring" for more details.
   
   
4. Center Diff Lock Indicator - On the Tacoma, the cluster indicator light is the only indicator you are in four-wheel drive. This is sufficient for the Tacoma since it only goes into 4WD locked when shifting into 4WD. However, since the MMTC has AWD and 4WD capability, we need some indication of which mode we are in. The controller grounds the output to the center diff lock indicator when it confirms the MMTC is indeed in AWD. See "Indicator Wiring" for more details.
   
   
5. Shift Position Switch - Unlike the Tacoma's controller, The 4Runner controller receives an input signal from the Transmission INDICATOR LIGHT SW [PARK/NEUTRAL POSITION). This switch lives on the exterior of the transmission on the passenger side. The controller receives a 12V signal from this switch when the vehicle is in drive. I spliced into the "drive signal" circuit near a connector above the glovebox. See "Transmission Shift Position Switch Wiring" for more details.
   
   
6. Output to Engine Control Module (ECM) - Unlike the Tacoma, the 4Runner's 4WD Controller sends an output signal to the ECM. Currently, I'm still trying to figure out why. It appears the signal tells the ECM it is in "Drive." The signal comes from the Shift position switch (see 4) and is routed thru the 4WD Controller first. On the surface, this doesn't make much sense. However, I didn't dig too deep into it.
   
   The "drive" signal on the Tacoma comes from the PARK/NEUTRAL POSITION SW and routes directly to the ECM. My best guess is that the 4Runner alters the signal when 4WD is engaged, which then the ECM alters the tune slightly for better performance. Ultimately, I left this unwired. Since it is an output, this should not hurt anything to leave this pin untouched.

The table summarizes the new circuits, the termination pin on the MMTC Controller, and the circuit wiring color in the 4Runner Wiring Manual. It also shows what color wire I used to make the connections to keep everything straight and for future me when troubleshooting.


The diagram shows the ultimate pinout of the new connections on the controller and the one wire that needs to be swapped from pin 18 to pin 5


TE Connectivity 175269-1 contacts are compatible with the 4WD Controller Connector


New Circuits are being added to the existing TTC controller connector to make it electrically compatible with MMTC. Note: This work is being done after routing all new circuits to the controller​

Splicing the MMTC Harness to the Tacoma Harness

As stated, the MMTC is 3-1/8" longer than the TTC. In addition, the MMTC has two new endpoints, the 4WD Position Sensor and an Actuator Limit switch. The easiest thing to do is splice in the MMTC Harness to the rear of the Low/Neutral Position switch breakout. Ensuring many times that the length was correct, I made match marks on both harnesses and made the nerve-racking cut. It would be too easy if the Tacoma and 4Runner harnesses had the same colors for each circuit. Below is a table of the circuits, their corresponding colors, and a diagram of the connections.


Reference diagram of wires that are spliced together


Highlights of splicing the MMTC Harness to the Tacoma's Harness

There will be two extra wires (not counting grounds). These are for the aforementioned new sensors on the MMTC, an actuator limit switch, and the "AWD" shift position sensor. I extended these two wires and made a breakout from the harness. I ran it along the T-case harness for a short section.

Instead of following the complicated routing of the entire OEM harness, I routed thru a new hole I made just behind the shift levers, approximately where the center console cup holders are. I used a rubber grommet that seals the harness penetration. The new harness breakout routes along the driver side of the shift levers, under the shift covers, and makes its way to where the controller is mounted. I used a P-clip to secure the harness breakout in place, which I discovered interfered with the shift lever trim cover. I notched the cover since that part of it gets covered by the center console assembly anyway.


Routing of the two new sensor wires ("sensor breakout")
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Lengthening the Vehicle Speed Sensor (VSS) Connection

The MMTC does not have a VSS installed in the rear output of the Case like the Tacoma (see the above post about swapping it over). The Tacoma uses the T-Case installed sensor for the speedometer, while the 4Runner uses the ABS Wheel Speed Sensors from the ABS/VSC system. We need to retain the VSS for the Tacoma speedo to work as intended. However, the VSS Harness Breakout does not reach and needs to be lengthened. I lengthened all three wires by 3.5". Just make sure you match the colors, and you're all good.


Lengthen VSS wiring by ~3.5."
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Dash Switch Mounting & Wiring

How are you to tell the controller you want AWD or 4WD? With a switch, of course. On the T4R, a center diff lock (CDL) switch is mounted to the left of the steering, near where we typically have our factory rear diff lock switch. In the context of this circuit, the switch acts like a SPST momentary "ON" switch (although it has more pins than needed suggesting it has more function than that). When pushed, the switch connects the corresponding controller pin to the ground, signaling the controller to go from center diff unlocked to locked or vice versa.

Side rant: Since the switch is a momentary "ON" switch, it does not latch, which I find annoying. I prefer the switch to latch (like the rear diff lock switch) since sometimes you're unsure if the controller "received" the signal.

I mounted mine next to the ECT PWR button, right under the driver-side vent outlet—the best spot considering my space, preferences, etc.

Examining the ECT switch hole, I noticed the switch was recessed into the dash to flush the switch with the panel. Damn, this is just a bit more complicated. Choosing not just to cut a hole and let the CDL switch stand proud and drive me crazy every time I looked at it, I took to CAD. I copied the geometry of the switch hole next to it; I made an adapter that I glued in with two-part epoxy. The result is imperfect, but you must stare hard to tell. That is good enough for me.


Would it really be a DIY project without the use of a dremel?


Great effort just to make the switch look plausible for a factory-installed option

The basic wiring is straightforward. Connect one side to the ground (color code white with black stripe), and the other goes back to the controller. I spliced into the nearby rheostat wiring, which has a ground wire. The contacts that are used in the switch connector are Yazaki 7116-4020.


Yazaki 7116-4020

The OEM pigtail I asked for only has two wires. However, the switch has multiple pins and even a bulb to backlight it. Apparently, Toyota engineering thought, "you don't need this switch lit at night," or Toyota business folks thought, "It's far too expensive to add two more wires and contacts." For extra credit, I will wire the switch to the dash illumination circuit, giving it that "OEM installed" feel. Pins 2 & 3 are the pins for the backlight. Reference diagram below:



I wired the switch and indicator onto their own harness since they share much of the same routing. Please reference at the next section, where I discuss this harness and routing.​

Indicator Wiring

But how will we know when the truck is in AWD or 4WD? Should we trust ourselves to remember and assume the truck shifted flawlessly? No, absolutely not.

On the T4R, a neat little pictogram display shows when the 4Runner is in AWD or 4WD. All four wheels illuminate green in AWD, and the center light remains off. When in 4WD (aka locked center diff), all four wheel illuminate, and the center diff illuminates orange. When in 2WD, nothing is illuminated.

I chose to go with the 4Runner indication scheme. I adapted the OEM 4Runner Cluster pictogram to work with this system. I contemplated a few different locations like embedding in the Tacoma cluster (too complicated and cluttered), putting in the OEM clock location (terrible spot for most things), or where the ECT Button was (not visible enough plug I wanted to put the switch there). Coming off or embedded in the A-Pillar seemed like the best of everything, although it would require some design work. I liked it best due to the visibility and the space behind the pillar to run wires. In the next post, I'll explain how I made and mounted the gauge. For now, let's focus on wiring it.


Gauge working during a system test before the interior's final assembly. Note: Gauge currently indicating the truck is in 4WD (center diff locked).

Regarding wiring, we need five: Two backlighting the gauge, a 12V ignition power supply, and the two wires to connect to the outputs from the 4WD controller. The controller grounds the respective outputs when AWD and 4WD are engaged.

As mentioned in the previous section about the switch wiring, the indicator and switch wiring share much of the same routing. I took the opportunity to test my electrical engineering skills, which are rudimentary at best—the harness routes between the CDL switch, gauge, and controller. The harness features an additional connector between the gauge and the rest of the harness. This is so the A-pillar can be removed in the future without having to cut any wires. Hopefully, the future me appreciates the extra effort past me did.

I made a few splices to get the dimmer (dash illumination), ignition power, and a ground. I used the ECT PWR switch wiring to get dimmer high (green with red stripe color code), dimmer low (white with green stripe), and ignition power (black with red stripe). I spliced the ground from the rheostat (the dimmer). See the diagram below.


Gauge Wiring Diagram


Harness fabricated with connecting components mocked up


Harness routing on the truck, with splices in adjacent connectors shown.


Drawing based on my desired routing and fabricated the harness using this as a guide. Verify your own measurements if you plan to follow this.
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Transmission Shift Position Switch Wiring

Lastly, the MMTC Controller takes an input from the transmission shift position switch, whereas the TTC Controller does not. The MMTC uses some control logic to restrict shifting based on transmission gear position. The switch lives on the side of the transmission, but instead of splicing a wire on the exterior and making more holes in the truck, I'll tap into the circuit where the body and engine harness meet. The circuit can be located above the upper glovebox liner. Remove the glovebox, and take down the lid for that space, and the connector is attached to the upper side. See the diagram below for reference:




Trans Position Switch splice and routing
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As always, feel free to add, suggest changes, ask questions, etc.

Stay Tuned, details about the gauge to follow soon.

 

DISPLAY PHASE:

The MultiMode T-Case (MMTC) has.... well, multiple modes. The Tacoma T-Case (TTC) has only one. On the Tacoma, this information is displayed with an indicator light built right into the cluster. On the 4Runner, a pictogram-type display indicates when the vehicle is in AWD vs. 4WD.


Display modes demonstrated on the 3rd Gen 4Runner

I really like the 4Runner's pictogram. It has that old-school Toyota look, displays the info we need, and will be a fun design challenge to integrate with the other displays.

I took apart the instrument cluster to see how the display works. The pictogram consists of two layers. One layer directs the light and changes colors, and the other is a clear outline of the driveline, which the light shines thru. The transparent layer also captures light from the cluster illumination, backlighting the gauge at night.


Instrument cluster components

Location

Ideally, the gauge is visible to the driver without much effort, doesn't look janky, and doesn't require too much altering of existing components. I considered a few locations and ranked them based on how much they met the criteria.

1. Gauge Pod on A-Pillar - Highly visible, medium complexity due to having to design an entire gauge pod and mounting system, only requiring holes in the existing A-Pillar cover.
2. Adjacent to ECT PWR switch - Decent visibility, still would need a gauge housing but less design work than the A-Pillar mount. However, I wanted to put the switch here, ultimately a close second.
3. Integrate into the instrument cluster - It would be sick to have it in the cluster just like the 4Runner, but it requires a lot of modification to the complex cluster and circuitry inside, which is unfeasible.
4. Factory clock - Easy to put there. The location is terrible. You have to do the right lean to even see the clock.

Locations Considered

Ultimately went with the A-pillar mount. At first, I was concerned the gauge would vibrate a bunch, as it is only supported by the thin trim plastic. But it turned out to be just fine. The gauge is super light, and the location doesn't vibrate that much to notice.


Design

There were a few design goals I had for the custom gauge.

1. Look "good enough."
2. Serviceable
3. Visible in sunny conditions
4. Backlit at night
5. No visible wires from the driver or passenger seat
6. Adjustable gauge face.

With those in mind, I took to Fusion 360 and started with the basics. No need to reinvent what Toyota did. I replicated a lot of the geometry in the 4Runners cluster for directing light into the respective lenses of the pictogram. Since the parts are ultimately 3D printed, I kept this in mind to avoid the annoying support material that is sometimes needed to complete the build.


3D Printed Gauge components vs. their model

The two layers of the pictogram are retained with two plastic pins in the cluster, then covered with a cluster lens. I designed the main body and cover it to replicate this setup. Each cavity in the main body is used to isolate light and direct it into the respective parts of the lens. Each hole allows the neo-wedge LEDs to pass thru from the board.

The gauge has two extra cavities on either side of the pictogram cavities. This space is lit with two LEDs. The clear transparency overhangs the other channels, thereby gathering light and refracting it across the picogram, giving it that backlight effect.


OEM Cluster vs gauge main body

I also designed a shroud to shade the gauge from direct sunlight, making the lights more visible in bright conditions.

The back cover houses the gauge circuit board (more about that board in the next section). The back cover is installed with three fasteners in countersunk holes to hide them and prevent any annoying bright reflection in the windshield. The fasteners thread directly into pilot holes in the main body. The fasteners allow the LEDs to be changed as needed.


Back Cover with Board

The mounting arm mounts the gauge to the A-Pillar with two M6 bolts. Once installed, the slot at the bottom allows for some adjustability of the up-down angle on the gauge. The end of the mount has fingers that mesh with corresponding fingers on the gauge body. It acts like a friction hinge and allows left-right angle adjustments of the gauge. Additionally, the mount has a channel and a corresponding channel cover. The wiring is routed from the gauge to the inside of the A-pillar. The wires are only visible in the gap between the gauge's back cover and the mounting arm.



Gauge final assembly


All parts were printed with ASA (an ABS derivative plastic). I selected this plastic due to its UV stability, and it can be acetone vapor smoothed, giving it a little less of that "3D Printed" look. An added benefit of designing in CAD is you can design dimensionally accurate tools to help you hand-build other parts, like the circuit board (see below). I printed a drill guide that allowed me to scribe the outline of the board and drill the appropriate holes in for the fasteners and LEDs.




Gauge Circuit:

If you have ever changed the bulbs in the cluster, you probably noticed the wedge-type bulb housings. Those housings take power and ground from the surface they mount to. If I want to use these types of bulbs and can change them easily, I will need to replicate this with my own board. No need to get too fancy here. A one-off prototype board will work great.

The bulbs are like surface mounted electronic components. I've used this technique in the past to make custom boards based on this video, and the techniques can be applies to this simple board:



I will drill holes in a circuit board for the LEDs to pass through and twist lock-in. The wedge is in contact with the board, so I must isolate that node ("pads", "islands") from the surrounding circuits. I used some 1/16" circuit board for this, as it was the correct thickness to work with the wedge lock.

The gauge board has effectively three circuits:

1. Four-Wheels: ON in AWD and 4WD (Center Diff Locked) modes. OFF in 2WD mode.
2. Center Diff: ON in 4WD (Center Diff Locked). OFF in 2WD and AWD modes
3. Backlight: ON with cluster illumination ON.

Depending on the LED, each pad gets either power or ground applied to it. The 4Runner's controller grounds an output depending on the mode the T-case is in. So, we need to supply a 12V ignition source to circuits 1 and 2. The ground for circuits 1 and 2 is fed back to the controller. The illumination circuit will be provided by tapping into another switch on the dash (see above post).


Creating the circuit board to illuminate the gauge pod


Wiring the circuit board

Based on the circuits, I scratched the board appropriately to make each of the modes isolated from each other. I then supplied the power and ground via wires soldered directly to the boards. Once soldered in place, I used some hot glue to ensure the wires stayed in place and didn't turn into a jumbled mess when installing the board into the cover.

Note: I realized later that I used the wrong color wire (grey) for the Center Diff Light, as another circuit in the system used this color as well. I later swapped out the gray wire for a pink wire to match the diagrams. So you'll see a discrepancy between the wiring diagrams and these pictures.


Mounting

Mounting the gauge was pretty straightforward. I mocked it up in a position I liked and roughly marked the locations on the A-Pillar Cover. I ensured there was enough clearance on the backside of the A-pillar cover for fasteners and routing of the harness.

Once I was happy, I drilled some holes in the plastic, and fastened it with M6 bolts and Nuts. I selected black bolts to minimize blinding myself with a shiny bolt in direct sunlight. Also, used washers on the backside of the pillar to prevent them from pulling thru the thin plastic over time. I also used a P-Clip on the backside to help keep the harness in place when installing.


Installing the gauge with its harness pigtail

Results

Overall, I'm pretty happy with the results of the gauge. Subjectively, I think the gauge is a bit clunky, but not so much so that it looks completely out of place. It definitely doesn't look like a hackjob, which is good enough for me.


Cool to see the digital model become real. Note: the back cover not installed in the photo, but you get the idea


Installed and working

If I had to do it again, I would spend more time sanding down some of the visible surfaces of the gauge, as you can still tell it's 3D printed if you look closely, especially on the face of the gauge cover.

In terms of visibility, the LEDs are visible in all conditions, but they do get a bit washed out in direct sunlight. In the future, I may paint the inside black surfaces of the gauge cavities white, which will effectively brighten the amount of light that shines thru the transparent layers.

 

HANG TIGHT - Future Results Documentation to be put here

 

Keep up the good work man! Awesome!

 

Dang

 

Hell of a write-up! Look forward to the video and updates! Very cool stuff!

 

Wow. Not many people would take this project on. I’d be willing to bet this has never been done before.

 

What are the odds... I was just mulling this over

What was your secret in locating a 4R that specifically had the multimode tcase?

 

Nice work!

 

.

 

Preach it.

 

This is the best. Sub'd for the ride.

 

Great write up so far Thanks for posting.

Best of luck getting this on the road .

This has long been on my back burner for something I wanted.

It was going to go on my 4x4 Celica.

Bad luck I was hurt and unable to work any longer!

 

Here’s a link to a thread from T4R explaining the difference transfer case options. Looking through it seem like any Limited trim from ‘99 and up had them , as well as all ‘01-02 models. ‘99-00s had the center locked as a position in the shift pattern, and the rest had a separate button on the dash.

 

Right, but no way aside from visually looking at every listing?

 

Most decent salvage yards should know the interchange between the cases and which vehicle the T-Case came off of. With the information about which 4Runners came with the Multimode, check out https://www.car-part.com/. When you search for a part, you can specify which vehicle you want it from. If there a multiple options for that year/make/model, it will ask you to specify which one so it can find the right case.

Also, check out this post by @turbodb , great reference for identifying the T-cases visually. https://www.tacomaworld.com/threads/1st-gen-transfer-case-identifcation-for-replacement-swap.753707/

I targeted '01-02 4Runners with automatic transmission. I believe those years came standard with the Multimode T-Case if it had 4WD. If at a pick and pull, look for the 4WD button on the transfer case shift lever and a center diff lock button to the left of the steering wheel on the dash.

I'll add the links above to the original post.

 

This is incredibly cool! Props.

 

Are you planning on documenting your length measurements for the rear driveshaft? If some specs can be nailed down, I think that would help people out a lot in doing this swap. That way they could acquire and shorten a driveshaft prior to getting into it.

I have been considering doing this but never saw enough documentation about it. The wiring doesn't scare me, it was mostly just physical modifications that might need to take place.

Are you planning on using ADD or manual hubs?

 

For the front driveshaft, use the donor's 4Runners shaft, it is already the perfect length for the MMTC. The distance between the front diff flange and the front T-case output is 30-1/8". Hard to get a good measurement of the actual front driveshaft, since it has and needs a slip joint.

The rear needs to be shortened by 3-1/8", as that is how much longer the case is compared to the Tacoma's T-case. I shortened the 1st rear driveshaft (between the T-case and the carrier bearing). After shortening, it almost exactly 27" in length from flange to flange.

I'm planning to stick with the ADD setup that is currently in the truck, I have had both ADD setup and manual hub setup at one time. I much prefer the ADD now.

One note that I'll add once I document the electrical controls. I believe your truck ('95.5-'00) uses vacuum-actuated ADD. The control system is likely different than mine, so I'm not sure how helpful this write-up will be. I just looked up just the 4WD computer for a '99 vs an '03, and they are indeed two different part numbers (89533-35110 vs 89533-35160). Not to say it can't be done, but might require some additional research.