Got this 85 a few months bacm from this old man that practically chopped up all electrical,doing lots of upgrades here and there. So when purchased, it didnt have the fuel gauge and I did notice the wires were spliced coming from the sending unit on the side of the fuel tank. I have 3 wires. Y/R, Y/B, and black wire.trying to hook up and aftermarket gauge. But when hooking up it shoots to full and the gauge stays on full even when the ignition is off. I ran black wire to the ground post on back of the gauge and then from the same ground post ran it to the negative terminal. Y/R figured it's the sending unit so I ran it to (S ) on the gauge . Ran ignition wire from gauge to positive terminal. And I left the Y/B unplugged since I think it's the low fuel light .so no the gauge shoots up to full , even when the car is off. If I remove the negative it still stays on full??? Took the ignition wire and hooked it to fuse and gauge jumps to full when ignition on and goes to empty when off. But it seems to be doing it without the ground even being hooked up to anything . I'm lost now. Anything helps guys. Try not to bash on me for the post lol