1976 D100
 

Fuel gauge not working.
How do I test to see if is gauge or tank sender?

Unplug the wire from the sending unit and ground it. See if the gauge goes to full.

I have an 89 dodge d100. Fuel gauge not working I pulled plug from tank and grounded it. Didn't move the fuel gauge, I have checked the wires and have not found any broken. When I check the plug at back of dash I can confirm I have 30 ohms with key in the on position in the fuel gauge pin. And when it is running I have .35 volts. When I connect the plug to cluster. And repeat same test to the pins on the fuel gauge itself it bounces around. And ideas where or what to look for would be greatly appreciated.

Those gauges are tested by a resistance meter. An old sending unit grounded will work too. A direct ground will risk killing the gauge. I know we often did it that way but it's risky. Those gauges have a voltage limiter that plugs into the circuit board next to the gauges. It's silver often with a black wire that looks like a condenser attached to it. They regulate the power to the gauges and often make the gauges do the koo ka rocha!!
https://cimg8.ibsrv.net/gimg/moparfo...ef1aefa382.jpg

Hello I saw the voltage limiter this one does not have anything attached to it.. I bought a new one to try it and didn't have any difference new one has a tab on the back of it m unsure if I need to ground it or not. Currently still have old one in, I am trying to trace this problem as I tend to forget to put fuel in for a long period of time and don't wanna run the pump dry to many times. Any other advice would be appreciated thank you

I think it's pointing at a bad gauge.

Any idea where I would find a new gauge.. I have browsed online like rock auto and stuff. But have come up empty.

For stock gauges the only options are NOS (New Old Stock) or used from a salvaged vehicle.

eBay is the first place I usually look. For example Part # 3635173

Alternatively, aftermarket universal gauges that operate in the correct ohm range (10 Ω to 73 Ω) are also available, but they really chop up the styling of the dash...

One last ditch effort before condemning the gauge is to try and re-calibrate it, I've had one come back by doing this. This video below is for different style of gauge but, the principle is the same by connecting a signal to the gauge and using the two adjustment holes on the back.

I'm not that good with electrical ect. Might have to have someone else take care of this for me. Thanks for the input