Hope this can help anyone that wants to use an aftermarket fuel gauge. May already be a write up on this but I couldn’t find it. I decided to go with aftermarket after not being able to find a cluster with one that actually works correctly.
Used one from Glowshift. Regardless of what gauge brand you use, results will be similar. After a few trials and error I got the new one working with no cel and gas lights on. I chose to mount the new gauge where the ashtray is. Didn’t take pics of how I wired power to it but I just used wire taps on the constant and switched ignition to the stereo.
Under the back seat I chose to just cut the green signal wire going to the fuel pump sending unit. With this wire not connected you will get a cel for high signal input. It uses a variable ground signal from the sending unit. You will also get the low gas warning light and dte will flash. I used a 47 ohm resistor and grounded the side going to the body harness and hooked the new gauge up to the side going to the pump. Ignore the butt connectors. This wasn’t the finished product. It was soldered after everything was working right.
If you ground the wire without the resistor, you will still get a CEL. After it’s all done with, my OEM gauge sits right above half and I have no CEL. You should be able to use any resistor between about 10 and 75 ohms. I opted for 47 OHM. Since it was in the middle of the resistance values of the sender. Last pic of where it sits with it all finished up. I’m happy with it.