Illum circuit fuse?

OP, the thing is since the ECT switch is out, I'm thinking it's an IC internal thing that "failed" because all switches have failed to illuminate. The ground junction mates all the switches grounds and the control to illuminate/dim is in the Combination Meter. You've verified power to the PANEL fuse, have you verified power to the connector of the removed ECT switch?

 

Great question, I will check the illum power to that switch and dive into the console tomorrow. Thanks to all of you for giving me some sensible next steps.

 

They're ground switched right? I was guessing it was some internal circuit in the ECU that popped.

 

Ground Dimmed...it's the illumination of the switch...

 

Well this is good news though I do not understand it yet. I did have power to the ECT switch for it's operation but not for the illumination wire. I dove and pulled the cluster, disconnected/blew out with small pressure compressor/inspected connection wires and pins on J5, J6, and the cluster main junction. I did not see any issue, but I am a tortoise and not the hare here so I plugging everything back in, reconnecting the neg batt terminal, and I tried another test....and well....success:

I am at a bit of a loss with this outcome. I was expecting to have to start checking wires to ensure nothing was broken or somehow cut/shorted but I now find it is working just as it should. I will be trying to do some more tracing to ensure there isn't a bare wire or nick somewhere that was related (though I am not sure what would have caused that). If I do not find anything I will stowing everything back together. Should I truly fine the root cause I will post another update. Plausible it was a loose connection or wire fault I have not yet seen that is at least resolved for the moment?

Thanks again for all the guidance!! @caribe makaira @Skydvrr @TnShooter

 

My guess is the disconnect of the negative. Electricity does weird shit man

 

The Main Body ECU is always powered via 10A ECU-B No. 3 (hot). It's very possible it "protected" itself when messing with the switches illumination circuit without disconnecting the battery ground terminal...

 

Well I am thankful it was not a costly venture. Thanks again for helping me out!

 

Caribe Makaira,
I am having the same problem on my 2017 Tacoma Limited. I went through all of the steps you suggested above, but I wasn't so lucky just disconnecting the grounding cable. Is there a way to check the Main Body ECU? Also the climate control LCD illumination lights go out when the headlights are turned on (see pics). Could this be tied to the auto light sensor in the dash?

 

There is, but that be a Stealership ta$k$.

Yes they are connected, but without more variables it's difficult to asses the issue. There is an OFF setting that can discard the unwanted/wrong feature, that way you can eliminate one angle.
The LCD should dim, not go OUT/OFF. Full bright when all lights are OFF.

What other signs are present?

 

When I put the cargo switch on the bench and test the illumination between the tan and green wire, the illumination light works. However, the voltage in the vehicle between ground and green is +13V and so is the tan wire +13V when the lights are turned on. This would indicate a short somewhere in the wiring correct?

 

No.
The circuit you are testing is the dash illumination, which can be adjusted from full brightness to nil. The Tan wire you are testing is part of a junction block where all the other dash lamps are joined. Testing to ground gets 13V dc because you are bypassing the dimming feature. You are risking ruining that feature.

 

I checked the voltage with a multi-meter, so hope that's ok. So if the illumination bulbs are good in the switches (Cargo switch, ECT, door windows, etc), what would be causing it to not illuminate when the lights are on. Sounds like the dimming feature isn't working now. What/where are the controls for the dimming feature...an ECU?

 

At this point the dimmer switch only dims and brightens the illumination on the tach and speedometer, nothing else. Where is the main body ECU located? Maybe I can start by disconnecting/reconnecting the wires. Your thoughts?

 

The Main Body ECU is attached to the junction box where the cab fuses are.

I would not start disconnecting anything. The Main Body ECU is always energized.

 

Is the light stalk in Tail light position while you tested the knob function?