The Stovebolt Site Forums The Shop Area The Electrical Bay Fuel gauge reading backwards?? HELP!

49 GMC 1 ton
Converting to 12 v
235 6 cyl
Original fuel gauge and sending unit
Running power through a resistor.


Okay you wizards of all things old trucks- I need your help! I recently tested my fuel tank sending unit and my fuel gauge to make sure they both worked before I install them in the truck. As info, I did check the sending unit,which came out of a 49 GMC 1 ton. It "ohmed" as you would expect throughout the full range of motion. They were hooked up as follows:

The sending unit was hooked up directly to the hot side on the fuel gauge. Power came directly from a 12v battery through a voltage reducer, to the power side of the fuel gauge, the ground wire came off the battery to the ground connection on the sending unit and also grounded to the back of the shell of the instrument cluster. Please note, I read every entry I could find in the tech tips section of the forum regarding the correct way to hook up a fuel gauge and sending unit. I certainly did not want to ruin either my sending unit or fuel gauge by hooking them up backwards.

Here's the problem, when everything is connected, and the sending unit is resting on empty, the fuel gauge is sitting in about one quarter full. However when I activate the sending unit to read a full tank,the fuel gauge needle actually moves toward the empty side of the gauge. In other words, the fuel gauge seems to be operating backwards! Please help an ol boy figure out what's wrong.

Thanks in advance