After extensive "Discussions" with the Ford Mechanic and service adviser, Mine finally got fixed.
I told them I thought it was a wiring problem, they insisted first that it was the fuel causing corrosion in the sending unit. Since I had Extended insurance, I told them to fix it, even though it was going to cost me the $100 deductible. After replacing the entire unit in the tank, to the tune of over $800, I drove over to the gas station 1 block away, and put in 10 gal.
the gauge was still hard over on EMPTY! Drove immediatly bact the the Dealer, parked in front of the main Service door, went in to the service adviser, and said" Fix the $*#@## thing right"
3 Mechanics(?) and the supervisor Had it immediately up on the rack, and after an additional 30 minutes, came and told me it was fixed. When I asked what was the problem, He said (in a very low voice) " It was a wire shorting to the Frame"
I said, "Noooo??" in My best disbelief voice.
After I got home, I put it up on My hoist, and found out what they did. The problem is in the connector attached to the frame beneath the driver door. Evidently water and what ever is on the road (In our case anti icing spray) can seep into the connector an short various connections. I have since had to repair My ground return wire which caused My Backup, Stop, Turn, and clearance lites to fail.
I highly recommend dielectric grease used freely on all the connections on this connecter. (And maybe an *** kicking to the engineer at Ford that put this connecter at this location.)