malfunctioning fuel guage

[janzpny]

I have a 99GT 281hp 4.6L sohc mustang. 118000 miles. When I took it off my sons hands it was bound for the junkyard. The fuel gauge didn't work so I did what I do on my bike and used the trip meter. Took the car in for new paint, put on a bbk cold air intake, new underdrive pulleys, clutch, rebuilt Tremec3650 tranny, flowmaster exhaust, pretty much everything and when I got it back the fuel gauge worked. Finally got to installing the fog lights and at the same time put a monster tach in it but DID NOT hook the tach up yet. Now the gas gauge is not working any more. I am assuming I need either a new sending unit or the computer needs reprogrammed. Any info is greatly appreciated.

Also need a little help with the wiring connections on the new Monster Tach if anyone has info on that.