Ford Repair: 98 Ford Windstar fuel gauge always shows, chevron techron fuel system, chevron techron fuel system cleaner

Question
QUESTION: Our fuel gauge remains on "full" all the time.  I've checked fuses and that doesn't seem to the problem.  Other thoughts on what I can check/repair/fix?  Thank you

ANSWER: You have 2 ways to start with, first. purchase 2 bottles of Chevron Techron fuel system cleaner. Add 1 bottle each time you put fuel in the vehicle. what can happen is sulfur builds up on the " card " in the fuel tank and sends erratic readings or replace the sending unit in the fuel tank. Obviously the first is the least expensive. Please keep me posted. -b-

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QUESTION: Thank you again for your advice.  I don't drive a lot so it took me awhile to use two full tanks of gas.  Your initial solution didn't work so presume it is the sending unit is the problem.  As I understand it, replacing the sending unit is expensive so do you suggest I simply track mileage using the odometer to know when to fill with gas?

Second, during damp weather, the sensor that the door is closed or the seatbelt is on does not appear to be functioning.  The ceiling light stays on and the sensor indicating there is a door open is lit.  The result is the chime stays on until I reach 15 mph.  Obviously it is very bothersome when it rains or is foggy.  Any suggestions?

Thank you again.

Answer
Yes, I think i would track the mileage, this is an expensive repair.. as far as the door light, try this.. most of the time it's the driver's door so. spray rust penetrant direct into the latch, slam the door a few times and then spray again and repeat. most of the time the switch in the door fills with dirt and debris casuing this