I rarely drive my 85GT after dark or in the rain but today I had to go to the doctor and it is raining.
In order to comply with the laws of NJ, I turned on my parking lights while driving and the temp
gauge pegged to the upper right and won't move back down.
I turned off the parking lights and the needle returned to it's normal position and the gauge seems
to be is working properly as long as I don't turn on either the parking or headlights.
Anyone have a suggestion what may be the cause of this phenomenon?
I appreciate any advice I can get.
Thanks

I guess no one has encountered this problem with the parking light/headlight switch affecting the temp gauge.
Thank you to the 20 people who at least read it.

[This message has been edited by QCMANAGER (edited 10-17-2020).]

Sounds like a "sneak path" problem.

I'd check the connectors on the back of the cluster.
Remove them, check for corrosion and reseat them.

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3.4L Supercharged 87 GT and Super Duty 4 Indy #163

Thanks, I will check the back of the panel.

Ever since I bought my 88GT my temp gauge was always pegged out and stuck, so I took everything part and unstuck the needle and it went back down. But whenever i turned the key to electrical it would jump then once i turned the key all the way when the starter engaged it pegged out and got stuck again. I found a form talking about how the wiring was not correct from the factory so i had to rewire the temp gauge to the temp sender. long story short it fixed the issue and my temp gauge always works now. here is the form http://w.gafieroclub.org/temp_gauge_repair.shtml

Goodluck