Fresh Wire To Sending Unit

My gas gauge sorta worked when I bought the Jeep but now its totally dead. Thinking of running a wire between the sending unit and the gauge to test. I am assuming that the gauge will have the one wire from the sending unit and then a wire powering it from the ignition switch is that right? So I could run a fresh wire from the sending unit and also hit the gauge with 12V to test? Also, I see a ground has been added to the tank so I don't think I have a ground issue but I can replace that too.

 

you can test it . by momentary touching sending unit wire to ground
needle should start to sweep . gauge is good .
fuel gauge has the voltage regulator built in . they do go bad
What you never want to DO is apply 12 volts to cluster . if it's not grounded to dash
voltage regulator will go poof . both gauges won't work

 

The wiring harness should have a connector somewhere between the dash and the sending unit. Follow the wires until you find where the chassis harness disconnects from the frame harness. At that point you can disconnect the two halves and test the gauge and the sender separately.

You will need a multimeter to test the sender. The sender will have a variable resistance between the wire and chassis; should be 72, 23 and 9 ohms for empty, half and full resp. That's all the gas tank part does.

To test the gauge, you will need some resistors of those values. It's easy if you have a couple of clip leads and the resistors. I made a tester - shown here Build A Gauge Tester - but all you really need are the resistors and some clip leads.

There is a constant voltage regulator (CVR) that's in the fuel gauge. If it quits, both your fuel gauge and temp gauge should stop working. If either works, you can assume it's ok.

About the ground thing that Ron pointed out - the CVR is primitive. It regulates by turning 12V on and off every second or so. If you disconnect the cround from the cluster (ie remove it from the dash) and interrupt the ground to the dash, the CVR will not cycle and stay on all the time. Your gauges can not stand this for very long, and will burn out. So don't "hit the gauge with 12V" without understanding the circuit.