Expert: Brad Sears - 4/6/2008

Question
QUESTION: The fuel guage on my mustang does not work.  The person that I purchased the vehicle from recently replace the fuel tank.  I am not sure if the issue is in the wiring or the sending unit.  Any suggestions on how to verify which is the issue and the what to do to correct?

ANSWER: Is the fuel gage on full, empty, or somewhere in the middle?
Brad

---------- FOLLOW-UP ----------

QUESTION: stuck on empty

ANSWER: Ah ha, this indicates an open in the circuit. It could be as simple as the wire disconnected at the tank, a poor ground between the tank and the chassis, an open in the dash unit. The simple test is to get to the wire at the tank and disconnect it. Ground the wire and turn on the key. If the gage climbs to the full mark the wiring, and dash gage system are all ok and the problem is in the tank or the ground.
Brad

---------- FOLLOW-UP ----------

QUESTION: I disconnected the wire at the tank and grounded the wire.  The gauge climbed to full, so no issues with the wiring.  Where would/How would I check to insure the the tank is grounded properly?  And, could the issue be with the sending unit itself?

Answer
Ok, good report. Now we need to ground the fuel tank. I have several long, and I mean long jumper wires in my tool box. Use a little sand paper and get a good ground on a corner of the fuel tank. Then I using one of my long jumpers connect the other end to the negative terminal of the battery.  Make sure that the wires to the tank unit are all connected and turn on the key. If the gage shows the amount of fuel in the tank then the ground is your problem but if the gage still does not move the problem is in the tank.
Brad