How to Bench Test Temperature Gauge

[GTHawk]

Used the resistor method on my 62 hawk. Works very well, Use a small 1/2 watt carbon resistor from radio shack. I don't remember the size, between 10 and 100 ohms. Cut the wire coming from the sender to the gauge. Insert resistor but first slide some shrink tape up the wire to cover the resistor. It then is barely noticable.

[pdrnec]

The temp and fuel guages on my GT both rise when the headlights are on?

Your dash is made of fiberglass - the instruments all rely on a good ground to function properly. I'd look at the grounding of the instrument panel first.