Issue w/dimmer on stock radio...

[Jamison]

I bought my 02 Tahoe back in March and it was bone stock. I changed out the radio for a Pioneer AVIC-N2 that I had laying around and left the rest stock other than replacing the speakers with Memphis. Long story short, I went to put my subs and amp in the truck only to find out that the Pioneer pre-outs were bad (all 3 sets, must have been the harness) and I wasn't going to be able to use that unit anymore for subs. So, I decided to put my stock unit back in and use a Schoshe pre-out converter for RCA's for the amp. I tapped into both sets of rear speakers for the unit and everything sounds great. However, for some reason when I turn my headlights on now the radio and the radio knobs dim so much it looks as if they're off. Any suggestions on what's going on or is it my crappy luck?

 

[Jamison]

Update - I found another stock radio and plugged it in thinking that would fix my problem, but it didn't. Same thing, turn the headlight switch on and the radio display and buttons go out. The radio still works, I just can't see anything.

Anyone have any idea what's going on?