Accidently posted this over in performance, just reposting it here.

About a month or two ago, the Service Engine, ABS and Trac Off lights were going off on my 04 sunfire, took it to auto zone, they plugged into it and said they couldnt see any problem, so i took it back to the dealorship, they said that my wiring harness was bad and needed to be replaced, charged me 300 bucks to replace it, now about a month later its doing it again, any ideas on what the problem could be?