Need help! 1989 mustang

The only thing I got out of all of this is its a 1989 Mustang, it's been converted to a carburetor setup, a fuel pump wire had to be grounded to get it to work, something about the fuel pump relay under the seat, the gas gauge used to work but now does not, and you modified the wiring.

I have no idea what your problem or problems are other than the gas gauge does not work. Take some time and provide some detail (what motor is in it, what modifications you have made both wiring and any aftermarket parts), use punctuation, and define what the problems are.

This is the only way we can help because we are not physically there looking at the car. Pictures would also be a huge help.

The ECU commanded the pump to turn on through the tan/light green wire with a ground. Here is the ECU wiring diagram which shows the wiring for the fuel pump in the bottom right:



Couple of things to think about here. There is a fusible link at the starter relay under the hood that provides 12V+ to the fuel pump relay and the ECU relay at all times. Check and make sure you are getting power to both relays and this would be the black/orange wire on both of them. If not then you need to locate the fusible link and see if it is blown. If you do have power at both relays then turn the ignition to the "on" position. You should now have 12V+ at the fuel pump relay on the black/orange wire and the red wire. If you do not have power on the red wire check the ECU relay and see if it has power on the red wire. If not then I would suspect the relay is bad. If you do have power on both wires at the fuel pump relay then ground the tan/light green wire and see if the pink/black wire has 12V+. If not then the relay is bad. If is does have power then its either wiring to the pump or the pump itself. There is one connector in the driver side kick panel that can have issues and the pink/black wire passes through it. There is also a connector back by the rear bumper and just above the fuel tank that is know to get corroded and cause issues which also has the fuel sending unit wiring in it.

Being you pump doesn't work and the fuel gauge doesn't work I would start with the connector back by the rear bumper and just above the fuel tank.



Looks like this when the tank is out of the car (courtesy of Mustang5L5):





They are known to get water in them and have issues. Inspect, clean if necessary, put dielectric grease in there, and reassemble.