Fuel gauge not working 1971 Dodge Demon

Posted this in the restoration forum Figured Id post here if thats more appropriate

Pulling my hair out for a friend here!! Little background. Fuel gauge hasnt worked on this car for years. Owner replaced the fuel tank fuel sender had the resister checked which Im told is good. Sender wire disconnected and grounded to gas tank strap gauge goes to full Key on sender wire disconnected and attached to a test light it flashes intermittantly which Im told is normal in both respects.

Now heres the kicker......if I remove the sender and attach the wire and ground the sender it functions by hand down empty up full. As soon as I submerge the float/sender in the tank it ceases to function I've looked in the filler whole and operated the float with a long screwdriver thru the filler hole and it has plenty of clearance and doesnt bind Tried numerous ground locations but no luck. I checked the cluster and the gauge cluster has a good ground as well. Im at wits end with this :-(

I had one do that once. It worked fine moving it up and down. Mine had the tinest hole in the float. it would take on just enough gas when in the tank it would stay sunk. You might want to test the float.

I did check that I submerged the floats in water no bubbles and no gas in either float

Attach the ground strap with the clips that go on the sender nipple and the fuel line . The world doesn't need any more bald people

Personally I throw the factory ground strap away.I attach a wire with a small hose clamp then use a sheet metal screw to the body.Never have any problems with them after that.The sender wont ground thru itself.You need the strap or run a wire to the sender nipple.Rocky

Yes Im using a wire with two alligator clips no matter where I ground itI get no response in the tank Ive grounded it metal line to metal line and the body Only works out of the tank No obstructions in the tank

Run a ground from the battery to the outlet.If that dosent work it almost has to be the float.Put the sender assembley in a bucket of water and see if the float arm moves.It dosent take much for them to hang up or be heavy.Rocky

If the sender is grounded then as said it has to be the sender assy itself (float/windings etc). I would fill the tank all the way up & if the gauge ain't pegged (Full) then it does not have a good ground because when the tank is full the rheostat windings are submerged & that is why the gauge is pegged with a full tank & it stays there for awhile before it starts to drop as the fuel level has to get below the windings so there's in effect no more dead short & it starts reading thru the actual resistance of the windings

sorry, don't think so.
gasoline is not conductive. or very minimally. shouldn't cause a short like that.
that is why you can have bare wires on a fuel pump in the tank. the windings usually aren't sealed either.

I would check the sending unit with a DVM and slowly move the float up and down it's full travel

Maybe the wiper is loosing contact against the windings.

that is actually a good idea.

see if you pull the float in an odd direction if it pulls the arm away from the windings.

it might be you manually moving the arm, it stays in contact, but when it floats, it pulls the contact away from the windings.

i had about that same problem, it was a bad float. i knew the wiring was good, gauge was good, dash volt regulator was good, ground was good, tested the sender with an ohm meter... still the gauge never got above ~1/8.

$11 for a new float on eBag fixed it.

Now i watch the gauge go down down down from full very quickly

Ive unclipped the brass float from the sender and shook it.To check it