The fuel gauge is stuck after i got alternator changed.How to repair?Pls advise?

most likely the sending unit/float/switch has gone bad.this is what tells you how much fuel is in the fuel tank.most fuel pump assemblies come with the sender built on to the fuel pump assembly,but yours is different,and is on the opposite side of the fuel tank from the fuel pump,inside the fuel tank.these units go out on all makes,models,whether bmw, chevy,ford,etc.this has nothing to do with the shop r&r your alternator.to make 100% sure that the sender is bad,you can get someone with a scan tool to verify that the sender or your gauge is bad,and most likely it's gonna be the sender.most anything you have done to this car is going to be from a few hundred quid to a couple thousand quid. Part Number 16 14 6 752 370 Fuel Level Sending Unit - Right Side - Genuine BMW $ 98.95 http://www.bavauto.com/shop.asp