The Old Man

Okay, I've got a problem. My coolant temp gauge has started to go crazy. Once the truck is warm and I turn on any lights the temp gauge moves up. Sometimes just a tad and sometimes almost to 2/3. Again, when it's warm and I shut off the engine and turn on the lights the gauge goes right on up to H. Turn the ignition on and it drops right back to 1/3. It doesn't drop if I turn the ignition to accessories. Any suggestions on where I should start looking? The battery is new. This just started this summer. Since I'm going to get gauges would I be smart in getting adding a mechanical coolant gauge? :

Thanks for any help :

Redleg

Start by cleaning the connections. Mine jumped all over the place til I cleaned it. If it's playing around when the lights are turned on, probabaly som ebad grounding.

The Old Man

I was afraid you might say something like bad grounding. But being an optimist I was sorta hoping else. Guess it's time to start looking.

Thanks for the info and have a great day. :-