Gage reads overheat when headlights are on

[jcskokos]

I'm not sure if this is a new problem or not because I didn't link the two conditions until now. When I turn on my headlights the temp gage will rise very quickly showing almost a catastrophic overheat. I will turn off the headlights in the same trip without pulling over our changing anything else and the gage will drop to a normal reading. I have ran through Google and couldn't find anything useful on the issue. No coolant leaks, new radiator, thermostat and water pump are maybe 3 years old. Vehicle is a 1967 coronet 500 4 door 383/727.

 

[440roadrunner]

This likely is right in the instrument cluster. I'm not familiar with the layout / wiring of those clusters offhand. If you or anyone could post a good clear photo of the rear of the cluster, that might help.

Mopar clusters have a horrid reputation for grounding. One thing I'd do is run a pigtail from a ground point on the cluster, and ground it to the steering column.

 

[black64]

Sounds like a body ground issue. Check grounds at cluster to body and body to engine.

 

[mopar 3 B]

Just tighten the cluster screws and see if the problem disappears. You have a bad ground at the cluster.

 

[bigmanjbmopar]

Yep ground issue or bad connection on the circuit board, I have seen this before on my 69 bleed over from a bad voltage limiter.

http://www.mymopar.com/downloads/1967/67CoronetA.JPG



Try this, in the parked position turn the key on but do not start, then turn on the headlights the problem should still be the same, if not than something else is causing it. Try the turn signals, brake lights as well with the headlights on and off etc.

While you are at it with the key on confirm the other gauges like fuel is reading correct while turning on headlight switch. just some checks to do.

 

[jcskokos]

Haven't had a chance to pull the cluster, but I did add a ground strap from the batt negative to the radiator support where a few grounds from the firewall mount up. I also found the battery had shifted and was kinkin that harness. After doing that the gage reads still a little higher when the lights are on, but not as high.
It seems that the problem occurs when the light switch is pulled out at all. Seems to happen more drastically in the morning or with cooler weather

 

[bigmanjbmopar]

It's not weather. Bad switch or bad ground.