Fuel sending unit

[steelworker77]

Fuel gauge started reading pegged full no matter what level it's at. It happened after filling up from basically empty. Filled it at the gas station and drove 3 miles home and checked resistance at the sender and was getting 6.7 ohms. If I unplug the ground wire it makes no change at the gauge. If I swap the wires it makes no change at the gauge.

Did the sender short out internally?

Any other tests I should do?

 

[Oldtimer]

If harness unplugged from sender, what is gage reading?

 

[steelworker77]

Reads empty. Needle doesn't budge if sender is unplugged

 

[DirtDonk]

With the ground disconnected and the gauge still reading full, it sure sounds like a shorted sending unit to me.
I don’t know that I’ve actually ever seen or heard of that happening, so can’t say that it’s a thing. But you pretty much eliminated the rest of the harness by disconnecting the unit from the system.
Since the gauge reads empty, the short is not ahead of the connector.

 

[Oldtimer]

Early Ford Bronco gages expect the sender to have a range of 10-73 ohms.
It is possible the float arm is stuck in the full position.
6.7 ohms is close to expected 10 ohms.

I would run the tank down to below half, and go for a drive, at speed, over a 1/2 dozen speed bumps.