It's happened to my truck twice, both since the original sender got replaced with a new factory part.

The pin (middle one?) will read exactly 100ohms, or the signal for empty. One time I dropped the tank completely, one time I just loosened one half and used a jack to lower the other side down enough to get my hand in there to unscrew it and wiggle it around.

When it happens again? I'll just drop the tank. It's a good chance to clean the junk off the top to avoid rust.

My Truck: 1987 XtraCab DLX 22R 4WD 5 Speed Manual
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"Speed has never killed anyone. Suddenly becoming stationary, that's what gets you." -Jeremy Clarkson