I've got this posted over in the audio forum too, but since this is definitely an electrical question...

I've got a USA Spec aux-in adapter plugged into the CD changer prewiring. The reason I'm using this unit is because I have BOTH an iPod (that I prefer to use manually rather than using an HU-controlled interface) and Sirius Sportster 5.

Fron day 1, I've had awful noise which hasn't been solved even after Crutchfield sent a second unit. It's a constant buzzing. I tried ground loop isolators which didn't have any effect. So now, I've bought an in-line noise filter that needs to be tapped into the CD changer wiring's ground and 12v constant. Hopefully that will solve the problem.

Problem is, I've been looking for days to find which wires those are. I bought a test light, but I can't seem to get it to work (I'm no electrician! I even stuck the leads into the cigarette lighter and I still can't get it to light up). And I can't find any wiring diagrams online (I don't wanna pay for a service manual that I'll never use again).

I'm fairly certain the brown wire is the ground since I've seen a bunch of brown wires attached directly to the chassis, but I have no idea which is the 12v constant. Assuming the positive wires are in the same 3-wire connector as the brown wire that I think is the ground, that would probably be either a white/yellow/red wire or a red/brown wire. But I have no way of knowing.

ANY help in tracking this down for me would be SO appreciated!