Help Request: '16+ Blower Motor Resistor not Working on '08

After 220k+ miles, the A/C blower motor resistor on my '08 finally went out. After some reading, I decided to replace it with Toyota blower motor resistor kit P/N 82141-04Q80, which contains an updated blower motor resistor design (compared to the OEM part it came with), as well as a wiring harness with ~4" of wire and a square 4-pin connector (instead of 4-pins in a line). From what I understand, this is the '16+ version blower motor resistor, but has been approved by Toyota to use on the '05-15 Tacomas as well, because on the package I received from the Toyota dealership, the label said "2005-2015 Tacoma". It is a very different looking part than the OEM 2008 one that I pulled out of my truck; comparing them looked to me like comparing something out of a 1970's computer to a smartphone.

I hooked up the wiring as shown below, which I found in this thread here on TW.
https://www.tacomaworld.com/threads/oem-blower-motor-resistor-wiring.624320/

Old Harness -> (Fan Setting) -> New Harness
White/Blue Stripe -> (Hi) -> Solid White
White/Black Stripe -> (Lo) -> White/ Black Stripe
Green/Yellow Stripe -> (M1) -> Solid Green
Blue/Black Stripe -> (M2) -> Solid Blue

After I hooked the wiring up (and yes I've triple-checked that it's connected as shown above) I now only have 3 fan speeds instead of 4. Settings 1 and 2 (the lowest 2 fan speeds on the dash control) output the same fan speed, followed by a higher fan speed on setting 3, and the highest fan speed on setting 4. So instead of Lo > M1 > M2 > Hi, I have one of the following, I'm honestly not sure which since I don't have another vehicle sitting next to it to reference it against.

Lo > Lo > M1 > Hi
Lo > Lo > M2 > Hi
Lo > Lo > M1 > M2 (I doubt this because the highest fan setting is pretty high)
M1 > M1 > M2 > Hi (I doubt this because the lowest fan setting is pretty low)

I've found factory schematics from a 2006, 2015, and 2016 as shown below. The 2006 and 2015 schematics are identical, so I'm going to make the assumption that the wiring is the same from '05 through '15. If you compare those two schematics to that of the '16 schematic, the wiring conversion listed above appears to be correct.


B4 Blower Motor Resistor 2006 by Ryan Ward, on Flickr



B4 Blower Motor Resistor 2015 by Ryan Ward, on Flickr



B4 Blower Motor Resistor 2016 by Ryan Ward, on Flickr

I have not pulled the HVAC control module (the 3 knobs on the dash) to inspect that there's no obvious issues on the back of it like burnt connections, that's my next step. I also haven't replaced my blower fan assembly, looks like they're ~$120 for OEM, less for aftermarket.

Beyond that, any other thoughts or things to try? I thought about the possibility that the resistor itself is bad, but that seems unlikely. There's also the option of cutting the OEM part off and installing one of the Dorman or other aftermarket options. Only having 3 speeds isn't the worst thing that's ever happened, but it does drive me crazy to have something that seems so simple not functioning properly on the truck.

 

According to the schematics and also the way other people have successfully wired it, you have it hooked up correctly. It’s a funky voltage divider circuit. It’s not simply going through 1 resistor for low, a different resistor for m1, and a different resistor for m2. Low uses 2 resistors in series. M1 and m2 both use 2 circuits to ground using combinations of resistors. If I had to guess, I would guess you have low, low, m2, high. If that’s the case, I would suspect a problem with the green>green/yellow connections or the m1 switch. That’s all just a guess and I have no idea how to test that scenario since there are multiple circuits going on when things are working correctly. Good luck.

 

Yea admittedly I'm too much of an electrical dummy to fully understand how this circuit works. I don't understand why the B4 resistor shows "Hi" on one of the connections, because the "Hi" fan speed setting completely bypasses this circuit and doesn't go through the resistor at all (hence the reason only Hi fan speed setting works when this resistor craps out).

 

Yeah, the letter designations on the resistor are pretty dumb. Especially since the 1 labeled "LO" is actually ground.

 

Hey Ryan, did you ever figure this out? If not, my guess is the resistor is bad (assuming everything is connected properly). Measure resistance (on the resistor) from pin "A" to each of the other pins. They should all be different. My guess it that pin "A" to pins "B" and "D" have the same resistance. If those measurements check out, the resistor is good and I would look into your connections/splices (assuming everything worked fine before it "went out").

 

Installing a post-2018 Blower Motor Resistor in a 2010 Tacoma:

Here is the correct wiring:
Old-------------New
White/Blue----White
White/Black---White/Black
Green/Yellow--Green
Black/Blue-----Blue

If you’re not sure this pertains to your truck/resistor, verifying is easy.

First, a quick explanation on how the system works:
Positive power comes from the Battery, through a Relay, and then to the Blower Motor. The circuit is completed through the Blower Motor Resistor and/or the dashboard Fan Switch.
When the Fan Switch is turned OFF, it opens the circuit and the Blower Motor does nothing, though it’s still connected to the +12V power source (a fully charged battery is generally in the 13-14V range).
When the switch is turned to HIGH, the circuit is completed through the Fan Switch, but bypasses the Blower Motor Resistor. Try it. Unplug the Resistor and start the truck… The Blower Motor will still function on HIGH, but turning the Fan Switch to any other setting will open the circuit.

LOW, M1, and M2 won’t function without the Blower Motor Resistor.
When the Fan Switch is set to M2, that wire is switched to ground and the current goes through a small Resistor.
When the Fan Switch is set to M1, that wire is switched to ground and the current goes through the same small Resistor, along with a slightly larger Resistor.
When the Fan Switch is set to LOW, the current goes through the same small Resistor, along with a large resistor. LOW is always connected to ground.
It’s basically a simple puzzle utilizing the concept of electricity following the path of least resistance.

Anyway, here’s how to verify you’re connecting properly:
Unplug the Blower Motor and Blower Motor Resistor.
Turn on the ignition.
Measure the voltage across the Blower Motor connector to find the pin with the line side power source (measure from this point for the next steps).
Set the Fan Switch to LOW.
Measure from the Blower Motor connector to each point on the Blower Motor Resistor connector. If you read voltage, that wire is LOW – Mark it.
Set the Fan Switch to M1.
Remeasure the Blower Motor Resistor connector points. You should still read voltage on the LOW wire, but you’ll also read voltage on another wire… That wire is M1 – Mark it.
Set the Fan Switch to M2.
Remeasure the Blower Motor Resistor connector points. You should still read voltage on the LOW wire, but you’ll also read voltage on another wire… That wire is M2 – Mark it.
One wire will never read voltage.
***If these steps didn’t work as I’ve described, you could have a bad connector. Cut off the connector, strip the wires, then remeasure. If there’s still an issue, there’s probably a problem with either the Fan Switch or the wiring between the Fan Switch and the Blower Motor Resistor connector.

The new Blower Motor Resistor is labeled as A, B, C, D. The connector itself is labeled as 1, 2, 3, 4. This is a breakdown of how the wire colors relate to the letter and number designations.
Blue – 1/C
Green – 2/D
White – 3/A
White/Black – 4/B

Before connecting, verify the Blower Motor Resistor configuration makes sense by measuring the resistance between these pins. I imagine there is some variation, so don’t worry too much about the numbers being exact. Here’s what I read:
A-B ≈ 2.7Ω
A-C ≈ .6Ω
A-D ≈ 1.5Ω

If good, connect the wires:
Connect the LOW wire to “B”.
Connect the M1 wire to “D”.
Connect the M2 wire to “C”.
Connect the remaining wire (the one that never read a voltage) to “A”.

After swapping the Blower Motor Resistor, plug the connectors in… Everything should work.

Here is an alternate form of wiring that would theoretically work:
Old-------------New
White/Blue-----Blue
White/Black----White/Blue
Green/Yellow--Green
Black/Blue-----White
***If you have connected it like this, only the M2 speed will be fused. This means you risk burning up wires, the Fan Switch, or possibly starting a fire behind/under your dashboard.

 

Although most of your post is correct, and it's obvious you have a very good understanding of electrical circuits, the testing you have described is way overly complicated and will go right over 99.7% of peoples heads.

1. There is no black/blue wire. You have that reversed. It's blue/black.
2. On M2, the current goes through 1 resistor, through the switch, to ground. But, some of the current also goes through that 1st resistor, through the resistor next to LO, and then to ground. The resulting fan speed is accomplished with 2 paths to ground through a combination of 2 resistors.
3. On M1, the current is going through all 3 resistors in a basic voltage drop circuit that is common in electronics.
4. Your testing procedure is using +12V as a reference and you are searching for a grounded terminal to acquire a voltage reading. This is outside the norm and not understood by 95% of people. Although your test results are correct, I'm not so sure there would be different results with an improperly connected resistor.
5. The general concensus is that you match white/black to white/black and then you just ignore the stripe when you match other colors. This makes sense when looking at the different 2nd gen and 3rd gen schematics.
6. When you mention an alternate way of wiring, that makes no sense to include that. In other words, "This is the correct way, but if you want to wire it a wrong way, like this, it should still work". There is no reason that a white/black wire should ever go anywhere other than ground. As you mentioned, you are bypassing the fuse. The fuse in the resistor is there in the event that the motor windings short out, creating a high current draw, but not bad enough to blow the 50A HEATER fuse.

 

1. You are correct. I was simply referencing the colors. I probably should've phrased it as blue/black for consistency.
2. No. It goes through one resistor (A-C). Yes, it does go to the Fan Switch... I explained that in the section above.
3. No. It goes through two resistors (A-D).
4. In this case, Ground is the reference, as you are looking for a voltage differential. How the connector is connected is irrelevant, as you are only looking to identify which wire is which. Once identified, they are spliced to the new connector.
5. Yes. You've just repeated what I already stated regarding the wire colors.
***One note on the schematics: At some point, Toyota changed the design of the resistor. I'm not sure when this happened. Maybe they're being produced both ways... Maybe different factories? It doesn't really matter, but I didn't mention it because it's irrelevant in regards to identifying the correct wires and connecting them. The end result is the same regardless of resistor design. My Blower Resistor is an OEM Toyota resistor, yet the internal schematic matches that of the Chevy Colorado, not the original Resistor that came with my truck. This makes sense since some people have pointed out that the Tacoma and Colorado parts are interchangeable (including the non-metric screws used to secure it in place.
6. I mentioned this for anyone who thinks they have it wired correctly just because it seems to work. Why? Because I've read in a couple posts that people claim to have it wired a different way, but it still works. The point here is for them to realize their way is wrong, and understand the potential negative outcomes if it isn't corrected.

At the top, I simply confirmed the correct wire colors to splice. That should be all that's needed for the average person.
The testing procedure is intended for anyone who's blower doesn't work properly after they've spliced the wires (or for anyone who just plain doesn't trust me). It can be very helpful to track down where a potential problem could be (or not be).
As you mention, the testing may be too complicated for most people - I did try to keep it simple. I believe anyone owning a DVM is probably capable of carrying out these steps. Nobody needs to completely understand the circuit as long as they know what to look for.

 

M1


M2

 

Sounds good... Feel free to message me if you ever have any questions about it.