Got this from a good web site someone recommended here. Read the last two lines for testing. It says in a nut shell, if the guage does not move from empty, the guage is bad. The next line then says if it does move, the sender is bad. So if I do this test it reads damned if you do and damned if you don't. Do the test and the needle should or shouldn't move. If it does, the sender is bad. If it doens't the guage is bad. So either way this test will find something bad. I don't get it. Anyone know of a more simple test for the sender and the guage??? I'm totally confused by this one. Allen
Testing the Fuel Sender unit on a CJ
The sender should have one wire (pink) with voltage from the sensor's isolated center post. The tab style connector and wire is a ground to the frame. Make sure it has good contacts.
To be sure the problem is not the gauge, you can momentarily short the (pink) wire on the output of the sender to ground, and this should show up as FULL on your gauge. No resistance at all will peg the needle FULL (the whole 12 volts). DO NOT hold it long in this position - just touch it and release. If the gauge does not move from EMPTY either the gauge's wiring has an open circuit (no voltage, or no connection to ground) or he gauge and/or its voltage regulator is bad. If it does move, the sender unit or its wiring is bad.