Don't remove the cables with the car running. May have worked in the old days, but you could zap the ECU these days, big bucks to replace. LIke Ham said, use a multimeter. Are you planning a lot of audio upgrades? The 80 amp does just fine unless you are really loading the car with amps, screens, etc.
1995 325I, window tint, K&N, debaffled airbox, BMW #104 wheels, Nighthawk low beams, smoked side markers, smoked corners, smoked taillights, M3 stlye heated mirrors, various interior bits, Bosal cat-back.