Gents Ive been readin this post for awhile now. Ive restored many classic GM and Plymouth cars, and even a couple of military jeeps. They all one thing in common. Fuel senders were shot, didnt work right , etc.
You guys have it pretty much worked out: Typical ground probs, shot senders, leaky floats, etc. But the ONLY way you can see if your sender is actually THE prob, even if they are new, is to bypass all the ralted wiring and see if the prob still exists. You would be VERY surprised that somewhere in the wiring from the gauge to the sender is actually causing the prob, not the sender or the gauge itself.
First of all, lets agree that the senders and gauges worked properly when the cars were sold from the showroom floor. As the years go by, and as issues arose, everyone either changed the gauge out or the fuel sender unit or the ground strap Thats because these are the easiest parts to replace. But no one replaces the entire wiring (its just one wire) from the gauge back to the sender
If you have changed out the fuel sender, checked the gauge, and changed out the ground strap, take the time to disconnect the main fuel sender wire from the back of the dash. Then take a jumper wire from the guage directly to the fuel sender (remove the fuel sender wire at the fuel sender first). All you are doing here is bypassing the main wiring that has prob been there for 40 years. If that clears up the prob, you know its the original wiring somewhere causing the prob. I have found this to be the actual prob on numerous older cars
