Oldsmobile/Buick Repair: Fuel Gage, 3800 engine, fuel tank

Question
Tom,
 I have a 1998 Olds Intrigue with a 3800 engine. The air conditioner was not working. I took it to a repair shop and they replaced the condenser. It works fine. However as my wife drove it home, she noticed that the fuel gage was not working. There is a peg about a quarter of an inch to the right of the "F". The needle is tight up against this peg on the other side of it. In other words, the needle has gone around counter clockwise and stopped up against the peg. It makes no difference if the ignition is on or off. I checked all of the fuses that I could find and they all look ok. I disconnected the battery and the gage is still pegged. The repair shop said it had nothing to do with this problem. More or less said that this is my problem and would not try to fix it. Could they have switched a wire some where or removed a ground wire? Any help would be appriciated.    Thank You.

Answer
I have heard this problem several times under numerous different circumstances and the fault in this case also was not caused by the ac shop.

The fault was usually traced back as to a faulty sending unit in the fuel tank.

NOTICE: However, do NOT go and replace the sending unit in the fuel tank until you have had the old sending unit and the dash gage TESTED by a professional automotive technician, Because the dash gage may also have been damaged by the sending unit and if you just install a sending unit and the gage is also bad, It will destroy the NEW sending unit.

Have the system FULLY TESTED FIRST.