I am having trouble getting my fuel gauge to read right. I swapped in a carburated 350 in place of my 2.8 and now my fuel gauge is screwed up. What are the three posts for on the back of the gauge, ground, 12V, and a resistance wire to the sender? My gauge will either peg to its max or peg to its minimum dependent on how a hook up the wires. Any help would be greatly appreciated.

 

Ironic, perhaps, but OTC used to make a tester/simulator for thermal fuel guages. They may still.

The variable resistance connection is to the tank sender. Check the resistance of the tank level sender with an ohmmeter instead of connecting the guage. There should be between 0 and about 90 ohms from the sender to ground, depending on tank level (float position).

 

The resistance read 3 ohms, but the peg is verticle and not pegged. Am I losing resistence somewhere?

 

You can simulate the float level sensor with a 100 ohm potentiometer. The problem is that it should be a 1W pot to handle the heater current of the guage. 3 Ohms may be correct depending on the fuel level in the tank.

You other choice is to replace either the guage or the float/sender in the tank to see if that's the problem, then possibly replace the other if you guessed wrong. A pot will be a lot cheaper than a float and guage, and certainly a lot easier to rig up as compared to dropping the tank.

 

Assuming there is a connection on the fuel tank sender wire, find it, and ground the gauge end of that wire. It should peg the gauge. If it doesn't, the problem exists "before" the tank. (wiring, gauge, etc) If it does peg, you've got a problem either in the sender, or the sender wiring.