Whenever I turn on the dash lights, my fuel gauge drops by 3-4 gallons. This also happens when I use my turn signals. What could be causing this?

 

Anytime I see erratic electrical problems I think bad ground.

 

Or other bad connections under the dash and at the gauge clusters.

 

Carry a fire extinguisher until fixed!! Battery cut-off would also be good!
An ounce of prevention-------

 

My car does this as well sometimes after starting it...the gas needle will go all the way to the fullest possible mark I just give the gauge a sharp rap with my knuckles and it goes back to where its supposed to be...

 

Every 63-64 FSC I've ever seen does this after so many years. Both my Starfires do it. Aggravating, but not enough to make me tear the dash apart.

I expect unplugging the printed circuit pin connectors and lightly cleaning the pins would help, but there's a risk of breaking those pins and that's no fun.

 

Hello Everyone,
Ground, Ground, Ground!!!!
While most of the world worries about am I getting power it is no good without ground!

I could be a bad printe circut board or wire wound resistor on the instrument cluster board, (also called a regulator) but ground the cluster dieactly to the battery with a jumper wire and I bet the problem goes away!

Good luck
Rich