gauges rise when I turn on the lights

Finally got the latest money pit on the road. now shaking out the problems.
Tonight's problem. When I turned the parking lights on the temp and oil gauges started slowly rising. At idle the oil was at 80 and the water which is usually 175 was around 200. went down as soon as I turned the lights off.
It's a 69 Charger, using the same gauges and headlight switch that came with it. All new wiring harnesses.
Is this some type of resistance or grounding problem??

probably grounding problem.
I would add a wire to the dash frame and maybe from the circuit board to the dash frame. see if that cures it.

or chase the holes the stuff bolts to.

Last time I had a problem like that the body ground was loose. I would check the body ground to the battery and or to the eng. Good luck , Ron

I think the instrument cluster grounds through the screws that hold it to the dash so if you have any paint behind them it won't ground.

I agree with these guys...likely a ground issue.