1998 Honda Prelude problems

Okay I bought this 1998 Honda prelude off this dude his son had a big speaker and amp hooked up in trunk he had ran a big blue cable Thur car moving the ECU carpet and other stuff to go to battery. Car quit running I immediately disconnected faulty hookup at radio and battery and had to buy a new battery, car started working again. Two weeks later speedometer went out, it wouldn't shift out of drive without assistance, battery life dim. I replaced the alternator and replaced starter. Car worked again for a month then it started doing everything all over again. I've checked alternator its good, starter is good, battery was drained I had to recharge battery, fuses are good, so what's wrong with this car