I had that problem when I first got my ho, ended up being the reverse light switch, which can be found on the tranny. I went through two of them, one was broke when I get the car, and the new one I got I think must have been bad, because it only lasted a few months, the one I got now seems to be holding up ok.
But like said, check the easy things first: bulbs, fuses.
__________________

02 Alero - ecotec - 5 Spd - Springtech springs - KYB GR2 struts - CAI - Sacchi
S1 lightweight 17s - Eclipse CD5435 - Sirius radio - 6000K HIDs - LED markers
|