Need help with fuel gauge not working?

Pretty simple, and there is tons of posts on this.

I assume you don't have a Ralleye cluster? (That is you only have a temp and fuel gauge, no oil?)

The two gauges are fed power from a regulator variously called voltage limiter, gauge regulator, IVR, etc. It plugs into the rear of the cluster.

What this means is, FIRST determine if the TEMP gauge is working. If you are not sure, use an alligator clip lead to ground the temperature sender wire. Switch the key to "run" and watch the gauge. It should quickly head on over to the "hot" reading. Don't leave the key on longer than needed, a few seconds.

If that works OK, on to the fuel gauge.

There are two ways to access the fuel sender wire. One is to remove the left kick panel and find the harness connector going to the rear harness. You need a shop manual which you can download free. You can probe the sender wire and ground it for the same test as above, or you can separate the harness and check the resistance of the sender to ground

The readings depending on fuel in the tank are variously:

L = 73.7 Ohms (empty)
M = 23.0 Ohms (1/2)
H = 10.2 Ohms (full)

The other way is to access the tank underneath, IE jack up the car. There's a connector at the sender, pulls right off. As above, you can ground the wire and check the gauge, and or you can check sender resistance.