96 jetta, runs rough with alternator plugged in, unplugged its great.

My buddies 96, or 97 jetta runs rough with the alternator plugged in, and if you unplug it, it runs great. Tried new battery, alternator, engine etc. He didn't replace the wiring harness yet though. Anyone ever heard of this?

Thank you.

hmmm,maybe check alternator 1 more time. or got a short in harness?

I agree. There must me a short somewhere in the wiring. What you can do is get a multimeter and hook one end to the wire that goes to the car and hook the other end to the output of the alternator and read the amperage. This will tell you how much power is being drawn from the car and prob if you have a short in the harness. Make sure you have the multimeter on a very high setting because cars pull a lot of amps.