Lights causing gauges to rise

[NHCharger]

When I turn on the parking lights or headlights it causes the temp and oil pressure gauges to rise. Doesn't do it when the car is cold, only after it is warmed up. The temp rises 20º, oil pressure 10 lbs. This takes about 3-5 minutes. I haven't left the lights on any longer for fear of a short. Someone suggested poor ground to dash. I attached a wire from a screw on the bottom back side of the dash to the steering column support but no difference.
Could it still be a bad grounding issue? Headlight switch slowly crapping out?

[303 Mopar]

Bad ground somewhere.