Well here it is, the orange gas ga wire looks like it's wire doubles back in the #15 tab on the connector plug that goes into the backside of the instrument gauge panel. 1971 had a flex printed circuit strip on the back side where as earlier had wires going to the gauges itself..Remove plug hook an ohm meter from it to where it connects at sending unit if it shows zip it open some where in between..with key off that is.. my 2cents
orich

 

I can't figure this out either. I put a brand new sending unit in, so its not the sending unit. The gauge was working at one point but I had no lights at all when I bought the truck and took it to a local shop. They were about to get all my lights working, but the fuel gauge hasnt worked since. Not sure what it could be. I have a tester and I tested the orange wire going to the sending unit and I have nothing. Could this be a fuse? I looked on the woring diagram, but it shows the orange wire going from the sending unit to the "Printed circuit circuit connector" What ever that is. I don't see it going to the back of the cluster anywhere.

 

the orange wire should be going to the plug that plugs into the back side of the dash, I think it's #15 if, I remember right on the plastic plug tab..
The dash lights our the screw in type that make contact with the c-board.
orich

 

I inspected the ground wire going to the sending unit and it was barley together. It looks like it was cut and put back together. I touched it and it fell apart. If I repair that wire could that solve my problem?

 

No ground no worky! think about it, why would it have a ground wire if not needed..
orich

 

Let's start over and go back to troubleshooting 101 because I can't seem to make sense of what's been done and what hasn't.

First question: Assuming that you have some gas in the tank, what does the gauge do when you turn on the key? Does it stay on E? Or does it go to F? The answer to this is fundamental to the subsequent troubleshooting path. Further questions to follow after we know the answer to this one.

 

When I turn the key its stays on "E".

 

Remove sender an hook up orange wire. Hook up a jumper ground wire to sender. Ok with the key on Hold sender as it would be in tank, slowly move float arm to about center, gauge should move as you move float arm. If no movement. Remove orange wire and touch to ground still with key on. Now gauge should go to full when grounded. if wires and gauge is good.. orich

 

I'm on the road and doing this on my iPhone so if there is any misspelling that I don't catch, please bear with me.

Good. Now we know that there is no current flowing through the circuit. This is NOT a shorted wire; rather, it is an open circuit.

The following simple test will isolate the problem to one of 3 areas: power, gauge or control (tank unit segment).

Test for power on both posts of the fuel gauge. Simply put one test lead to one post of the gauge, the other lead to a good ground. You'll find it may be anywhere between 0 and 12 volts, depending on whether your temp gauge is also operating, because of the voltage regulator unit. Also remember that the "regulator" is really just a betallic switch that turns the 12v on and off, so it generally averages about 12v. Make sure you connect your voltmeter and watch it for several seconds each time to allow for the switching of the regulator. Remember to chech power on both termonals of the gauge.

So here's the next question: Did you find power on both posts, one post, or neither post of the gauge?

(If this is too basic, please say so but I have no idea what your skill level is.)

If you have no voltage on either post, you have a problem with the circuit providing power to the gauge.

If you have voltage on one post but not the other, you have an open circuit in the gauge (bad gauge).

If you have voltage on both posts of the gauge, you have an open circuit between the gauge and the ground after the tank unit.

Post back with the results and we'll work step 3.

 

I meant to say that the regulator switches between 12v and zero volts, to provide an approximate average of 6v, not 12v.

 

Okay. I ran a test on the regulator in the back of the cluster. No resistance. I went to a junk yard and took a shot on another cluster. ($30) I tested the regulator on that and got a reading. Switched out the regulators and the gauge works now. A new regulator is 50 bucks through LMC so I guess I didn't do too bad and now I have some extra gauges if I need them.

 

I too am having a problem with no power going to my sending unit.where does the power come from in the truck for it to read the gas

 

By the way i have a 1975 ford f-250 highboy