4WD Dash Light Hack. Illuminating the light after a J-shift 4WD conversion.

For all you who have done the 4WD conversion the following is how i got the 4WD dash light to illuminate after the conversion without using the ECM. This is based on a J-shift transfer case, manual hubs & AT. It may work on other set-ups but not certain.

edit: See post #3 below for info on ADD system by @mechanicjon




First off i want to thank the following for helping me through this. No way i got this done without their help.

@BartMaster1234
@mechanicjon
@Uphillshunter

These guys helped me (and i am sure rolled their eyes a few times) in my 4WD thread where i did most of this research.

I wanted to put out a separate thread on this though so others can find this little hack alot easier.

Tools you will need.
- Harness
- Soldering Iron
- Solder
- Electrical Tape
- Wire snips
- Wire strippers
- Phillips Screw Driver
- 10mm driver
- Flat head screw driver or upholstery removal tool.
- Flash Light
- Factory dash bulb with holder.
- Zip ties
- 2 hours.

This is the schematic we worked up to do this hack.




These are the factory references. We are trying to tie into IK2 and we are looking for Pin 3 which is a Green/Black wire. There are other places you can tie into too. For instance behind the dash or in the drivers side kick panel but i wanted somewhere easy to get to and where if i had to check it out later i did not have to take the dash apart.








The harness was pretty easy to build if you have the equipment. Time to install was about 2 hours and requires pulling the dash apart, the shifter console out and of course routing the wires from the transfer case into the cabin.

I do have two extra harnesses available if you want to do the same. They are not cheap but PM me for info.

The transfer case has three switches. The harness wires all three in parallel so if any one is switched the dash light will illuminate. You will not know which mode of 4WD you are in (4H, N or 4L) but i do not think you normally do anyways.

A little back-ground first. The switchs at the transfer case is just that, switchs. There are three. 4H, 4L and N. As stated the harness just wires them all in parallel so if any one is switched the circuit is closed. The 4WD bulb we will place in your dash already has positive power routed to it. That is there is a place for it in the dash and it already has wiring in place. It just lacks a ground which normally comes from the ECM when one of the switches is closed. We just have to put the bulb in and route ground to it. Simple.

The harness.
I used factory plugs and pins. Harness is sealed connector to connector using heat shrink tubing and then overlaid with protective mesh. The goal was to prevent oxidation. The rear of the connectors are sealed with silicone. I used 12 gage wire which is overkill but is what i had.








At the Transfer Case
There are three plugs. Two of one style (white) and one of another. (blue) You really cannot plug them in wrong. They are keyed and will not reach otherwise. Two are on one side of the case and one on the other. They are hard to photograph installed but they should be there. Plug them in.








Up into the cabin.
From the transfer case you will go into the cabin through the AT shifter plate. I did not want to poke a hole in the AT shifter seal or the Transfer case seal so what i did may sort of crush the cables a little but it works. Do here as you see fit.

As an aside i tried real hard to figure out the original wire routing. It was all in vane though. I am pretty certain that non-4WD trucks do not have the connector in the Engine compartment so you have to route it some other way.

Moving on.

Remove the center console and the shifter plate cover.




Unbolt the ten 10mm bolts holding the plate to the tunnel and lift it up a little. Now back under the truck and push the harness from under the truck into the cabin.




Once the harness is all the way in go back under the truck and secure the harness to whatever is convenient with zip ties. I used the VSS extension cable i made as part of my conversion.




Back in the cabin notice on the front right side of the shifter assembly plate there is a indent in the plate. This is where i positioned my cable and clamped it in place when i re-tightened the mount bolts for the shifter assy. This provided a very shallow passage for the cable not to be totally crushed.








Up into the dash area.
From the console i simply ran the harness under the bottom of the lower center dash console and headed towards the glove box behind whatever is down there in the foot well. I did not have to take anything apart here but you will later take the dash apart so you may want to do that first to route this cable easier.

Under the console. FIRST REMOVE YOUR BATTERY GROUND CABLE! We do not want any accidents here.




Remove the glove box. (Two Phillips screws at the bottom hinge.)

Remove the upper glove box cover. Three 10mm bolts and one light cable. You have to sort of pull the sides of the cover in and down to remove this cover. This exposes the ECM and some white connectors. The cover will hang from these connectors. That is fine.




Notice two things. There are a few large 10mm bolts near the ECM and there is a large white connector and two small connectors on the cover you just removed.

One of the wires from the harness will go to one of those large bolts. Cut the wire to length and strip the wire back. Loosen one of these bolts and stick the wire under it. Re-tighten. That is your ground tie in. There are many place to get to ground so if you do not like this one find another. Also it does not matter which wire you use from the harness. I used the blue one.




The other wire is going to tie into the rear of the larger white connector on the cover. You are going to have to cut into the wire so get yourself prepared.

NOTE!!!

If you are gun shy you can ring this cable out ahead of time if you want to. Take the dash apart at this point and locate the connector shown later in this thread. Check continuity between IK2 #3 and the wire on the dash pod. It should ring out.

You are looking for pin#3 on the far right or back side of the large connector. No need to disconnect it. The wire green with a black stripe and is labeled #3 Double check you have the right wire!!! Cut the wire and splice the two cut ends and the other wire from the harness together. (White/Red in my case) Tape them up for protection.






Technically speaking you are working with Connector IK2 and pin #3. Note do not go in from the left side. Use the right side.


The dash bulb.
There are a few threads already on how to take the dash apart so i will not cover that. I used this one from @turbodb (If you do not want this linked i will remove it)

https://www.tacomaworld.com/threads/how-to-dash-trim-removal-1st-gen.528257/

Take out your dash pod. There are four Phillips screws and three connectors.

Turn the pod over and notice the following open light hole. That hole on the other side has the green 4WD indicator. What we are trying to illuminate.




This light bulb routes to this connector which then goes to the ECM through the Green & Black wire. That same wire you just tied into that goes from here to there. (I did ring them all out which is how i ended up down at IK2, pin #3.




Install your new light bulb here and install your dash pod.

At this point you may be able to test your lighting before you put the dash back together but honestly i did not try this. I just put the dash back together because all we did here was install a bulb.

Now, the dash is apart so if you were not happy with the routing of the harness before you can correct that now.

Put it all back together and you should now have a 4WD dash light when you shift into 4H, N and 4L.

Happy trails.

 

Great write up. PM sent your way regarding one of the extra harnesses you have.

 

Your running manual hubs correct? If some one was running a ADD axle that needs to be tied inline after the rest of the switches.
Great write up.

 

Yes. Manual hubs. I forget that J-shift was available for ADD too although i have never seen one. I have edited my statement above. Thank you Jon.

 

Great write up - It's one thing I never bothered to address after my conversion.... One of these days...

 

Well done. I went the extra mile on my conversion and actually replaced the unused ABS and RR DIFF LOCK lens with 4HI and 4LO lamps after I made a custom lens in Photoshop. That’s why I have those on the schematic above.

 

Finally wired this up after like two years. I had to de-pin #3 and re-pin at the bottom of the connector. Mine was routed tighter under the other wires and I couldn’t pull it out to splice into like in the pictures above.

 

Glad it worked. Mine has been trouble free since installed. Can't say i have done alot of trail work in the last 2 years but that light still works...

 

If anyone is interested i am going to build up a few more of these harnesses. Mine has been trouble free since 2019. PM me.

 

Im wondering if anyone can shed more light on @BartMaster1234 4wd diagram? I understand that he customized his ABS and RR DIFF LOCK lights with "4hi" and "4lo" but my question is how? If all the grounds of the harness are connected together, and all the "positive" grounds are connected together and spliced into pin #3, how do I also tap into the ABS and RR DIFF LOCK pins? more wires? This is a whole new ballgame for me, so visually I dont understand how to wire the 4wd light to stay on while also having the "4hi" and "4lo" lights turn on while switching between gears.

 

So the cluster is negative switched. All the indicator and backlighting is constant 12vDC, and if you want a light to turn on (such as ABS, RR DIFF LOCK, Low Fuel, Seatbelt, etc.) you simply ground that circuit.

All the sensors in the transfer case are doing is completing a ground. So you need to wire the RR DIFF LOCK and the ABS circuits on the cluster directly to the 4HI and 4LO sensors. However, the transmission cannot differentiate between 4HI and 4LO, it just says whether it's in 4WD or it's in 4LO. So when you're in 4LO, both indicators turn on.

I recommend you wire the 4WD indicator (the stock one) in parallel with the 4HI and 4LO indicators, the way it is in my diagram doesn't work properly with the diodes.

 

Okay so I get that I wire one wire from 4HI sensor to ABS circuit and one wire from 4LO sensor to RR DIFF LOCK circuit, the other wire from the sensors go to chassis ground. That completes the 4HI and 4LO switches.

I’m having trouble understanding how to wire the 4wd indicator in parallel with the other indicators.

 

Simply add two extra wires from the two sensors and wire them to the stock indicator. IMO you don't really even need it, it's redundant since you already have a light telling you 4HI or 4LO now. OP's method made the truck's indicator function as factory, my method really only stipulates if you're in 4HI or 4LO. The 4LO sensor's only purpose on a stock truck is to tell the RR DIFF LOCK not to engage unless the truck is in 4LO. It was not connected to any indicator.

BTW - if your truck does not have ABS you will have to solder a 3" jumper wire to bypass the missing ABS module in the cluster. Follow the copper trace, and add a wire where it's missing.

 

woah. my simple mind is blown.

Yes! In my research I came across this post by you:
https://www.tacomaworld.com/threads...st-gen-edition.138573/page-6707#post-16844870
This will allow me to tap into the ABS wire and use the ABS blank?

Thank you so much for the clarity so far! Really appreciate it

 

You can actually get by with 1 extra wire from the 4WD position sensor, that was its original purpose.

 

Made a modified schematic that’s a bit simpler for me to understand. I figure since Im going to make my own indicator lights, I might as well put the factory 4WD indicator on the left side of the cluster in place of “CRUISE”. That way I have RR DIFF LOCK, the 4WD indicator, and 4LO on one side.

I honestly have no plans of doing this right now but, just for future references, I thought I’d at least write it all down. Let me know if it’ll work or not cause i have no idea!

 

Good explanation on the working principals. Useful. Thanks

 

@mjhenks sick right up. Thanks

 

Here is a companion post by @Area51Runner that illuminates the A/T P dash light near the temp gauge if you truck happens to have this light too. My truck does not but still they go hand in hand.

https://www.tacomaworld.com/threads...and-a-t-p-neutral-light.783875/#post-28047084

 

Im almost done with my conversion, and I bought the neutral switch for my tcase so I can do this too, and get all the wiring done all at once.