Hey:
Got a small problem. I just installed the APC wireharness upgrade. When I turn on the headlights the left side low beam does not turn on. Right side is fine. High beams seem to work OK on both sides. Need help on fixing this problem...Anyone? Fernando

 

First, try switching the two relays that comes with the kit. Each relay controls one side of the car's headlamps. After you switch them, and you see that not the RIGHT highbeam is bad...then it's the originally left relay that is no good.

If your LEFT highbeam is still bad after the relay switch, try switching the bulbs. If the bad highbeam now goes to the other side, your bulb is no good.

Finally, is all else fails, check the wiring of the harness to see that the connectors are good, and if any of the wires have been severed anywhere.