Fuel gauge... How does it work?

[ak7]

Okay... So let me know if I have this right. I've been checking out the Autometer gauges and came across the fuel gauge, which I will be replacing in my truck. My fuel gauge seems to move but only when it wants to. This is completely not my area but I believe there is a sending unit in the gas tank? Now the Autometer fuel level gauge works off an ohm reading, 0 for empty and 90 for full. I'm assuming the gauge gets this signal from the sending unit, correct? I'm trying to figure out how to troubleshoot the problem with my fuel level gauge. I am also curious as to how I could get a 'Low Fuel' light installed. Somebody told me the light would hook up directly to the sending unit. Anyways, I'm lost and was hoping somebody could point me in the right direction.

ak7

 

[Klink K5]

On a gm vechile when you ground the sending unit wire to the chassis, the fuel gauge should go down all the way . When the wire is disconnected, the gauge should be past full. The sending unit in your tank could be bad to because the little wires your float wire runs across could be broke. {hard to explain over computer} I hope you find your problem.

 

[Muddytazz]

I had this same problem a while back, come to find out, all the problem was is the 2 or 3 nuts on the back of the gauge were loose causeing a weird connection, tightened them back up and its worked fine ever since.

 

[MontanaLifted]

The Autometer gauge works on the exact same principle as your factory GM gauge from the '70's.
{sending unit} Basically power is supplied to a piece of metal (known as a potentiometer). On that piece of metal is a "needle, or pointer" that is connected to your float. When that needle, pointer thing moves across that pice of metal it creates a different resistance(or OHM).
So if your tank is full of fuel the pointer is all the way to one side showing "x" amount of resistance. When it's empty it's on the other side showing the opposite resistance.
That's why when you ground your sending unit or disconnect the power lead your needle on your gauge will peg to one side or the other.
(I hope I didn't just make this overly complicated)