I had to disconnect the factory fuel pump wires on my GF's 89 RS when I swapped it to carb because the damn thing would only stay on for a few seconds then turn off, so I hard wired it to run by running a wire from the fuse box and spliced it into the fuel pump lines behind the back seat. Problem is now the gage doesn't work. Any ideas??

 

Easy, check behind the back seat, remove the carpet, there will be 3 wires, 1 gray, 1 black and 1 white I think, just take the white one and rerun the wire up to your fuel gauge.