Potential wiring problem

Gliderider · Oct 22, 2024

Hello folks. I’m currently having an issue where my coolant temp gauge is being “told” that the engine is overheating on my ‘83 C10. As soon as you turn the ignition on the gauge immediately redlines, even with a cold engine. The temp sensor itself is new. I removed the wire from the temp sensor and it has the same result. The problem started after driving over a very rough gravel road that bounced the truck around pretty bad. Is it possible that something came loose that would cause a false reading on my gauge?

AuroraGirl · Oct 22, 2024

Gliderider said:
Hello folks. I’m currently having an issue where my coolant temp gauge is being “told” that the engine is overheating on my ‘83 C10. As soon as you turn the ignition on the gauge immediately redlines, even with a cold engine. The temp sensor itself is new. I removed the wire from the temp sensor and it has the same result. The problem started after driving over a very rough gravel road that bounced the truck around pretty bad. Is it possible that something came loose that would cause a false reading on my gauge

have you had the cluster out lately?

CalSgt · Oct 22, 2024

Gliderider said:
Hello folks. I’m currently having an issue where my coolant temp gauge is being “told” that the engine is overheating on my ‘83 C10. As soon as you turn the ignition on the gauge immediately redlines, even with a cold engine. The temp sensor itself is new. I removed the wire from the temp sensor and it has the same result. The problem started after driving over a very rough gravel road that bounced the truck around pretty bad. Is it possible that something came loose that would cause a false reading on my gauge?

I’d guess the gauge wiring has a short somewhere.

Trace the wiring back to the firewall bulkhead, inspect for damage or chafing.

If no damage there look in the cab:

The harness that runs up to the gauge cluster from the bulkhead/fuse block is fairly large diameter and very difficult to get to. But you may be able to look for anywhere it may have been rubbing on a sharp edge. The gauge cluster wiring is the bundle that goes up the firewall not the bundle that glues up the column.

Gliderider · Oct 22, 2024

Have not had the gauge cluster out since I’ve owned this truck. I did have a problem a while back where the wire from the sensor had rubbed through and was shorting out which caused a similar problem and I fixed that. So far I haven’t been able to find any exposed areas this time around but that’s the only thing I can think of. Also, I did find a mouse in the cab a few months back so it is also possible that it chewed something and it is just now becoming a problem

CalSgt · Oct 22, 2024

Gliderider said:
Have not had the gauge cluster out since I’ve owned this truck. I did have a problem a while back where the wire from the sensor had rubbed through and was shorting out which caused a similar problem and I fixed that. So far I haven’t been able to find any exposed areas this time around but that’s the only thing I can think of. Also, I did find a mouse in the cab a few months back so it is also possible that it chewed something and it is just now becoming a problem

Mice love wiring insulation for some odd reason

Gliderider · Oct 22, 2024

I have found some chewed insulation on the inside of the firewall but not on any of the wires. The previous owner had the motor rebuilt and when when he did the interior wiring he completely wrapped all the wiring bundles in electrical tape, I can find absolutely no damage whatsoever to any of those

CalSgt · Oct 22, 2024

Gliderider said:
I have found some chewed insulation on the inside of the firewall but not on any of the wires. The previous owner had the motor rebuilt and when when he did the interior wiring he completely wrapped all the wiring bundles in electrical tape, I can find absolutely no damage whatsoever to any of those

The factory wrap looks like electrical tape just less sticky

Gliderider · Oct 22, 2024

I’ll keep looking but I really need to be able to drive this truck, and it absolutely will not start or run if it thinks it’s overheating. Is there a way I can temporarily bypass this until I diagnose the problem with the wiring?

AuroraGirl · Oct 22, 2024

I accidently snagged the coolant sensor wire on my 1980 between the head and the valve cover , if you possibly did something similar worth a check.

Gliderider · Oct 22, 2024

I followed the wire all the way to the back of the motor where it goes into a sleeve, the sleeve comes back across the firewall behind the brake booster and then through the firewall. It’s not pinched or caught on anything and I can find no apparent damage to it under the dash.

85K304SPD · Oct 22, 2024

Gliderider said:
I’ll keep looking but I really need to be able to drive this truck, and it absolutely will not start or run if it thinks it’s overheating. Is there a way I can temporarily bypass this until I diagnose the problem with the wiring?

I dont think that '83 trucks "think". They don't have computers that would provide overheat protection, prevent it from starting, no matter what the gauge says, or if it even is hooked up.
Maybe you are having other wiring issues that are preventing it from starting.

Gliderider · Oct 22, 2024

Yeah that was a poor choice of words on my part. I was just trying to figure out what would cause the motor to quit and the temp gauge to redline at the same time. I keep thinking it’s a ground issue but so far I’ve found nothing

SquareRoot · Oct 22, 2024

Gliderider said:
it absolutely will not start or run if it thinks it’s overheating.

Lol. Say what? Sounds like it was way ahead of it's time.

Gliderider · Oct 22, 2024

Have to keep in mind that it still has the original wiring, and after 41 years some of it is kind of sketchy. I can’t afford a new wiring harness at this time so I tend to patch when and where it’s needed

Gliderider · Oct 22, 2024

SquareRoot , I didn’t phrase it correctly. I know the temp gauge has nothing to do with the motor shutting off, it’s just that those are the 2 symptoms I have to work with. Temp gauge redlines and motor shuts off, but it’s not overheating whatsoever

Potential wiring problem

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