Ground the tank sending unit directly to a clean chassis spot near sending unit. Do this by running a wire from one of the sender mounting screws to the frame (chassis) Make sure the screw is cleaned/wire brushed to shinny metal The gauge needs it's own ground wire straight to clean dash metal. Ground chassis to engine with good proper ground cable. Ground chassis to body. (remember there are RUBBER mounting pads between body and chassis) The engine is isolated from the chassis with RUBBER pads. of course you have the battery ground to engine, I'm sure. All of these old trucks need ALL of these grounds. If the truck is painted or rusted, the bolts will not carry the ground path, they are not meant to anyway. The no. 1 cause of malfunction of a gas gauge is the ground and that means the entire ground system.
You did NOT say if you tested the gauge/sender in the tank BEFORE installing into vehicle. You should have tested it all with a temporary ground and hot hook up. You need to know that it all works by isolating the sender and gauge by running test wires that are not part of the harness. Then you will know it's a wiring or ground problem and NOT the gauge or sender. Also, are you sure that your modified sender is not binding inside the tank? I have done what you did for my suburban, modified a truck sender (cut the pick up tube shorter and coil the float wire to make it shorter). Since you bought a 55-59 truck sender it would be the correct ohmage. Ground! ground! ground! Clean metal to metal!!!!!!! all around the truck!!!!!!!!!
ALSO when you "reversed" the wires during your test you could have burned out the gauge. Do not hook up a gauge unless you know for sure which is ground terminal and which is hot.
Last edited by bartamos; 08/18/2011 8:29 PM.
