how come my instrument lights and gas gauge dont work?

[70xr7cougar]

i have a 68 and a 69 cougar. on both of them the gas gauges dont work and the instrument lights dont work. my 68 has a new tank and sender so I assume it is an electrical or fuse problem? if someone has some insight that would be a great help...

[Ron67]

Sounds like a bad ground on instrument lights its grounded right under the clusters 1 screw in each you will see them easy maybe lose or remove them little sanding then try them see if it worked.had the same problem with my dash lights

[BOSSGTE]

The instruments lights go thru the headlight switch and a bad switch will cause this. Run a jumper wire to the instrument light fuse and see if the lights come on. If they do, it most likely is the switch OR some dummy
has cut the double grey wire plug connection going to light the original radio to install and light an aftermarket radio. They cut the wires at the plug to power and light the new radio not realizing that the other grey wire goes back to the dash lights. I believe the current flows from the headlight switch, to the fuse box, to the radio light and then back over to the instrument panel lights. I use a Standard brand light switch for a 1978 T-Bird I believe #251 or #351 and use the dash spacer broken off the old switch when I install it in my Cougar.

The gas gauge sender is most likely a Mustang single prong sending unit and usually the sending unit is the culprit. Make sure if your cars have low fuel light that the single prong Mustang gas gauge sender is pluged in the correct hole on the 3 hole Cougar low fuel connector to move the gas gauge.

Hope this helps...