I have discovered strange electical gremlins inhabiting either the light switch or the water temperature gauge...or both in my 1980.

The water temperature gauge acts and reads normally until I turn on either the parking lamps or the headlights. Then the needle will swing to the right and peg itself until I turn the lights off. The gauge will then go back to normal readings. No other gauges are affected. The light switch was replaced approximately 1 year ago, but I've never messed with the water temp gauge, which is original as far as I know.

Thanks for any advice or exorcisms in advance.

 

There is bad ground someplace, looks like its going to ground through your gauge cluster...just a thought

 

You don't have a gremlin. That's for sure. A gremlin is an intermittant as when a wire is stripped and taps against metal and shorts out (at the weirdest most unpredictable moments).

It sounds like the problem is consistant. If it happens the same way everytime, then its not a gremlin.

To fix it academically, you would need the wire diagram, the switch diagram and the water temp guage diagram. The water temp guage has a piece of metal that changes resistance with temperature. If the guage peps to one side, it is either shorted (zero ohms) or open (infinite ohms). Find out what the ohm reading should be when its pegged and you may find that when 12v is applied to a certain pin, the guage gives a max reading or vice versa.

To fix the problem, check the wiring especially around the light switch to see if a wire was crushed or frayed or twisted somehow. It could be a bad ground; maybe when it was iffy and when it was removed and replaced, it broke. Since the temp guage seems to be effected by operation of the light switch and since the light switch was replaced recently, start there.

I like these jobs because there is no heavy lifting. Again, just start by eyeballing the wiring and switch.

 

symptoms suggest bag Gnd thru the cluster.
it sounds like a poor gnd for the front light harness,
thus the little electrons seek Gnd via any place possible.
also verify your light switch is Gnded.
locate Identifiy every gnd wire on your car, and verifiy a solid connection.
good luck...69VETT