Headlight Switch Causes Temperature Gauge to Peg

[gcorsar]

My son was driving my car one late afternoon and switched on the headlights when he got on the highway. He then noticed that the temperature gauge was pegged to the hot side! Panic! But then he tried switching the headlights off to see if by some weird chance the switch caused the gauge problem. It did... Any idea why turning on the headlights would cause the gauge to go all the way to the hot side?

[azruss]

I have a similar problem. When I turn out my lights, my temp gauge starts reading 10 degrees high. I haven't tried to sort it out, but assume it is a weak ground. I was very thorough in cleaning all my wiring when i assembled the car, so somewhat surprised to see it.

[spider2081]

I know its a little difficult to get to but have you removed the internal lighting bulb from the temperature gauge and tested it?

The gauge and the light share the same ground and it is riveted to the gauge case. I soldered it to the case and it helped. I also modified the light socket so it had its own ground wire. The needle still moves about one needle width up but not as much as it did when I got the car.

[vandor]

Likely a bad ground to the gauge. My oil pressure did that when the ground connection was loose. I added a dedicated ground for the gauges (just tied it in to one of the gauge ground wires) and now the needles do not move when I turn on the headlights.

[gcorsar]

Well it could very well be a ground problem. I replace the bulb in the temperature gauge and now my driver side headlight doesn't work. I'll have to tear into the dash wiring I guess to do some more grounding.

[KandJinmaine]

I have a similar problem with our '80. I got home from a ride into town and back and when I shut the motor off the temp gauge pegged hot. I looked under the hood, checked the dipstick for mayo ( thankfully found none), and did some head scratching. I went inside the house and came back about 5 min.s later to see if it was the same.... That's when I noticed I had left the parking lamps and fog lights on, turned them off and the gauge went back to off.....

When I take the car apart this fall through spring I will do the extra grounding, and "brown wire fix".
Jeff