I need some help!! I've got a 67 442 n my fuel gauge is reading full all the time. I installed a new sender and I'm reading about 32ohm of resistance at the sender, that's good. Now I know my fuel gauge has three hook ups: one 12v, one ground, and one signal. With the gauge removed and key on I have 32 ohms at the signal input, good ground at the ground input, and 12v at the power input.....that's right too! Now I'm measuring the the ohms between the ground and signal input and the 12v between the 12v input and the ground input. I have also checked these with another ground to be sure. Now here is the weird part begins. With the key off, I read almost 700 ohms between the 12v and ground, key on and it's only like 8 ohms!! Sounds so weird, but if you look at the wiring diagram, the 12v source comes from the instrument fuse and powers and powers the cluster light bulbs and the brake idiot light on the side. Another thing is the 12v to the fuse in the fuse panel come from the ignition switch. After all that I'm feeling like I have a short in that 12v source somewhere, either in the headlight switch or ignition switch???
Now this all started after I mistakenly back fed the signal wire from the sender with 12v. So I forced 12v back when it's supposed to be sent to the sender. Now the sender is new and installed after I made the mistake!
Any help would be great
Ken

 

If you ground the wire that goes from the sender at the tank to the gauge, does the gauge go to "E"? This will prove that the gauge and the wiring are good.

 

I believe I did this and it went straight to full. How can I test the gauge?
Is no resistance empty and high resistance full?
Wait duh, it is!
I started with what ever was in the tank, that was at 8.2 ohms. Put almost 5 gals in and it was almost 20 ohms, then almost another 5 gals and it went to 32ish ohms. Both these readings are taken at the tank sender and at the gauge inputs, so I feel like my wiring there is good! I think my problem is that there should be NO resistance between the 12v input and the ground with key off. And that there is 8ish ohms of resistance with key on!! Right?

Any chance some one would be willing to remove their dash gauge pod and read theses two readings? It's only two screws! The left top screw is is the 12v, right top screw is the ground, and the bottom screw is the signal.....please?

 

If you have the gauge cluster apart, ground the negative side of the gauge, if it goes to E then you have to look at the connector in the front before it goes under the floor and the one in the trunk where it comes out.

The sender is just a big rheostat. Sorry but most of us do not check resistance or get really technical when it comes to the fuel gauge. The sender I think is 0 -95 ohms.

 

You can't measure resistance with current running through the circuit, so all of the measurements that you made with the key on are invalid.

You also can't measure the resistance of the things you are trying to measure with them connected to the rest of the car, or you are also measuring the resistance of everything else they are connected to, such as the dash lights.

You can measure the resistance of the gauge with the gauge completely disconnected from everything else, but, as OldCutlass said, there is no need to.

Your measurements of the sender resistance sound right - it should be 90Ω Full, 0Ω Empty, and somewhere in between for the rest.
If you ground the sender terminal, with or without the sender connected, the gauge should go to E.
If you disconnect the sender, the gauge should go past F to about 3:00.

If those things don't happen, you've probably got a bad gauge, so long as the gauge itself is getting 12v.

- Eric