brake pedal engine dies

ok i have an 86 firebird with a 2.8L in her and everytime i press the brake pedal the engine dies but she restarts right after. im thinking vacuum leak but have not found anything. also the problem goes away if i take off the positive battery cable (i was testing the alternator). any suggestions would be great thanks cuz im out of ideas:banghead:

Now when you say the engine dies...does it cut right off completely? electrical and all? Or does it just kinda bog down and stall?