Temperature gauge ...sensor or gauge, or electrical

[rsingle]

My temp gauge needle moves when idling ..but when I turn on the light switch for parking lights , and also headlights
The gauge pops to 220 degrees top of the scale .turn Lights off needle goes down to normal. 90 degrees .

Question. Is my temp sensor on top of engine block ( closest to firewall) not working ? Or is it a ground . Why do lights affect this gauge ? How do I test the sensor . No light goes on for over heating. Could the other sensor be gone also ? The front one .

Thx someone ...anyone have seen this happening ?

[spider2081]

My guess would be a poor ground at the gauge itself. There is a 4 pin connector about 6 inches behind the gauge so the gauge can be unplugged from the car. The gauge dash light and instrument share the same ground connection on the back of the gauge. It is a push terminal riveted to the gauge case. I had a gauge where the rivet loosened and the gauge indicated 10-20 degrees higher with the lights on. I soldered the terminal to the gauge case and that cured the issue.