Somewhere around 1989, Ford changed the resistance of the sending units. The earlier ones were 73 ohms empty, and about 10 ohms full. The newer ones are 16 ohms empty, and 158 ohms full. You can pull the sender out of the tank and easily check it w/ a DVM. Or, fill the tank and check it in place. You'll probably have to get w/ the Ford Motorsport guys to verify the gage. Then you have a choice, change the gage or change the sender, whichever is easiest and/or cheapest. Good luck!
