dont have any good info but ill throw out some ideas: Aftermarket Raido w/BU camera. Signal wire for the cam should be tapped into that, also ive heard but not too sure that there is a reverse wire signal in the rearview mirror, may only be with newer vechiles but ive seen it in some???Check possibly...Bulbs installed properly and correct rating/size/app???Again sounds stupid but who knows... If you still cant get it you could always run a new wire and bypass possilbe short and/or use signal from stalk and relay it to turn on the reverse lights, all this may sound good,bad right or wrong but another mind as work is always better than one. Plus ive noticed theres not a whole lot of traffic on here so ill throw my .02 in where i find suitable. Side note try to find someone that has an ALLDATA account im sure the schematic will be there...GL