what could this be?

[JDM_180SX]

what does this sound like to you, i went to start up my 1990 240 with 126k miles on it, my battery was dead, so i jumped started it, it started fine, but when i take off the jumper cables, the engine just stops. does that mean the alternator is shot?

[big jon's 240]

Yup, sounds like your alternator is toast. I would check your wiring first (could be a bad connection somehwhere) to be sure, but that sounds like a classic example of a bad alternator. Not to worry, a rebuilt alternator from a parts store should only set you back about 60 bucks, give or take.Do you have a mutlimeter? Thats the easiest way to figure out what your problem is. If you do, put it to your battery while you have the car jumped, if you get some descent voltage (above 10.8) then your wiring is good. If you take the cables off and the voltage drops significantly (which it probably will, since it dies), then you most likely have a hosed alternator.