I have a long term unresolved problem with 3 of my Stewart Warner Deluxe gauges. These are electric gauges not mechanical. My Tach, Fuel Level, and Temperature gauges all jump up a few points when the light switch is moved from off position to the parking light or headlight position.
When the lights are switched on:
The tach will raise 200 Rpm.
The fuel level will raise to show approx. 1 1/2 to 2 gallons of additional fuel.
The temperature gauge will raise another 15 to 20 degrees.

The ammeter is uneffected as are all other gauges which are mechanical.
All gauges are grounded with seperate and individual wires.

The only thing common to all 3 gauges effected and the light switch is the gauge lights that they all carry.

Any ideas are most welcome.
-Geary