Need help with my fuel gauge. I looked at the searches and they don't seem to apply to my 61 Dynamic. Gauge reads 1/4 tank when full and drops as fuel is burned.


Checked the wires at the sending unit, green with yellow stripe and green wire. When I ground the green wire (not center) the gauge goes to full. When I ground the green with yellow wire the gauge goes to 1/2 tank.


My understanding is that this gauge operates between 0 and 30 ohms.


Which wire is the ground? Should the gauge read full or empty if the gauge wire is grounded?


thanks for the help.

 

An open circuit will drive the gauge full, wire shorted to ground it will go to empty. Are you sure your gauge is wired correctly?

 

Oldcutlass describes the test you need to do. Remove the wire from the sending unit. With the ignition ON, the needle should go to F or beyond it. Now ground the wire. The needle should move immediately to E. If the gauge does these things, then it is fine and your problem is likely the sending unit.

 

Thanks, my sending unit has two wires? One is solid green the other is green with a yellow strip. The wiring diagram shows one wire should be gray and the other yellow. The gray wire should go to the gauge and the other I can't determine. Why are there two wires?

 

I would imagine the other wire goes to ground.

A bad ground is a common source of problems in old fuel gauge systems. The connection point becomes corroded, and the connection is intermittent or fails completely.

The gas gauge is a simple series circuit with the gauge (the indicator) and a variable resistor (the sending unit) in series. Once side of the gauge connects to +12V from the battery. The other side connects to one side of the sending unit. The other side connects to ground, completing the circuit. The sending unit is configured so that a full tank corresponds to maximum resistance, 30 ohms in your case, while an empty tank corresponds to zero resistance.

The fact that your gauge gets stuck at 1/4 even when the tank is full suggests either that there is a restriction in the movement of the gauge needle itself, preventing it from moving past 1/4, or the sending unit has gone bad and never moves enough to register more than 1/4 tank no matter how much fuel is in there.

But the first thing to do is confirm that the gauge itself is functioning properly, and the way to do that is as described above. Take the wire going from the gauge to the sending unit, disconnect it at the sending unit end (ignore the sending unit ground wire for now), and then put the ignition key in the ON position and see what the gauge does when you alternately ground the wire you just removed from the sending unit and then remove it from ground. Grounded, the gauge should point to E, and with an open circuit (which is infinite resistance), it should point to F or possibly past it (because infinite resistance is a lot more than 30 ohms).