How to bench test a fuel gauge.

[casper50]

I've searched but come up with over 100 non fuel gauge results.   Is there a way to test the 3 post 47 Dodge fuel gauge on the bench?  Still cannot get mine to work.  The sending unit is new and sends 0 - 20 ohms on multimeter. 

[casper50]

Right now tank is about 3/4 to 2/3 full.   At both the top of the sending unit and the back of the gauge both mounted in car I am reading 17ish ohms.  Original gauge reads below empty, the NOS that I just installed reads just off of E.

[knuckleharley]

I doan no nutting bout no lectricity,but MY "go to first" point is always the ground. Is your tank grounded? Is your gauge grounded?

[casper50]

It worked fine up until 2 weeks ago.  gauge is grounded through the screws to the cluster box and then to the body.  I can check on the tank.

 

[rekbender]

Did your solve your fuel gauge problem? I found this schematic and directions for testing a three wire Auto-Lite gas gauge (Dodge '39-'48) in a '49 Motor manual. It appears that current flows to the heating coil post at the rear center of the gauge, through the contacts on both the full and empty sides of the gauge,  through the two bi-metallic strips, and then through the two wires to the sender. If I'm reading them right, the directions say pulsing current should be present at tank sender connections terminal 1 and terminal 2 as the bi-metallic strips heat and cool, and open and close the contacts. Depending on where the tank arm is on the resistance, the strips on both side of the gauge reach a different, but steady state temperature, and move the gauge needle. The gauge doesn't ground through the dash, only through the tank resistance. With current to the gauge, clean gauge contacts, two good wires to the tank unit, and a good tank unit with a good ground, everything ought to work!

[casper50]

tks will work on it more tomorrow