91 Legacy Sport Sedan Electrical Questions

[redlineracer541]

I have a 91 Subaru Legacy Sport Sedan and everytime I turn on my projector headlights, the car drops 50 rpm in idle and when I was driving my car yesterday, I dunno what happened but I was going over rough roads for less than a mile and when I parked my car and turned everything off (I didnt have my lights on) I tried starting up my car and didnt even click over, then when I jump started it, it ran until I got it home and just died. I checked my battery it was completely drained of juice (I have a deep cell battery) and I jumped the car again and I found out my alternator was dead. How can my car go from running okay to just dying all of a sudden? When I got my car jumped from where I was at on the rough road my car ran very sluggish and it would cut out when I barely hit the pedal. I dunno if my electrical on my projectors is sucking out my battery or what. But I have a new alternator on the way and warranty the battery and I will see what happens. But I dont know if the amperage on the alternator has anything to do with it since it only runs 70 amps. I also have a sound system in the car and I had it hitting hard before the alternator went out and did a little off roading and towing.

[Jay!]

Alternator would be my first guess in general, but I don't know much about managing large mobile audio.