1990 c3500 coolant temperature sensor wiring question
 

Hey fellas I was wondering if anyone on here could tell me what color the 2 wires are for the coolant temperature sensor on the top of the intake near the thermostat housing? And also is one wire for signal and the other ground or are they both signal wires? My harness is all jacked up with connectors missing as the truck sat with no drivetrain for many years.. thanks again in advance

Re: 1990 c3500 coolant temperature sensor wiring question
 

Yellow & Black.

Yellow is the Signal.

Black grounds through the ECM.

Re: 1990 c3500 coolant temperature sensor wiring question
 

Thanks a bunch for your help sir! So the yellow signal wire will go directly to the ecm at pin C10 according to the ecm schematic correct? And what about the black wire does that go directly to the ecm aswell?

Re: 1990 c3500 coolant temperature sensor wiring question
 

You're welcome!

Yes the coolant sensor yellow goes to C10.

The schematic in the 1990 wiring manual shows the coolant sensor black goes to the ECM terminal D2.

Another GM manual I have shows it could go to terminal A11.

Which trans & engine did it have?

Re: 1990 c3500 coolant temperature sensor wiring question
 

This is the wiring diagram I have:

Re: 1990 c3500 coolant temperature sensor wiring question
 

It originally had the sbc 350 with th400 transmission sir

Re: 1990 c3500 coolant temperature sensor wiring question
 

After looking at a few different schematics, it looks to me like the Square body trucks used terminal A11 for the coolant sensor ground, and the GMT400 used terminal D2.

Re: 1990 c3500 coolant temperature sensor wiring question
 

Ok awesome! You rock man!!
So in theory if i can not find continuity with a meter on any wire on the engine side of the harness I can run the yellow and black wires directly to the corresponding pins in the ecm correct?

Re: 1990 c3500 coolant temperature sensor wiring question
 

Yes, running your own wires would be ok.

Re: 1990 c3500 coolant temperature sensor wiring question
 

Awesome! I might have to do just that. One more question if you don't mind me picking your brain a bit more sir: where does the single knock sensor wire go to? I don't believe I see anything on the ecm pin-out that refers to the knock sensor.. Unless I'm overlooking it ��

Re: 1990 c3500 coolant temperature sensor wiring question
 

On that vehicle I am fairly sure it uses an ESC module and the knock sensor connects to it. I will go look at the schematic again to make sure this is so.

Re: 1990 c3500 coolant temperature sensor wiring question
 

Yes that truck has an ESC (Electronic Spark Control) module that the knock sensor connects to. The ESC signal is sent to the ECM terminal B7

Re: 1990 c3500 coolant temperature sensor wiring question
 

That's on the wiring diagram I posted.

Your welcome.

Re: 1990 c3500 coolant temperature sensor wiring question
 

The diagram you posted does match what I am seeing in the GM service manual.

Re: 1990 c3500 coolant temperature sensor wiring question
 

Very good info! Just exactly what I need to get this thing back on the road.. so the knock sensor wire will have direct continuity to one of the wires going to the esc module correct? Then from there the signal goes from the esc module to ecm terminal b7

Re: 1990 c3500 coolant temperature sensor wiring question
 

Yes, terminal E.
Make sure that the knock sensor wire is shielded and keep it away from spark plug wires or anything else that can induce a voltage in it.
Yes

Re: 1990 c3500 coolant temperature sensor wiring question
 

It matches how my truck is wired. That's why I have it.

Re: 1990 c3500 coolant temperature sensor wiring question
 

Good deal! I will try to make some sense of everything today hopefully I can get it all going. I will chime back in with progress thanks again fellas for all your priceless knowledge

Re: 1990 c3500 coolant temperature sensor wiring question
 

Hey fellas nmjust wanted to say thank you to everyone who helped me out with my annoying wiring questions and also thanks for providing all the needed schematics!! My truck is bmnow running smoothly cranked right up on the 1st try after sitting for every bit of 5yrs with no front clip and no drivetrain! You guys rock!

Re: 1990 c3500 coolant temperature sensor wiring question
 

You're welcome!

Glad you got things taken care of.

Thank you for the feed back.