Ok, so I took my aftermarket radio out to make some minor adjustments, and when I put it back in - no workie. After some multimeter testing, it seems I am not getting a voltage drop between the ground and the +12V from the harness. Between a metal part of the car and the +12V of the harness works like a champ though. How or what could have caused this? Should I simply wire my ground wire to a metal part or is there something more sinister lurking behind the dash?

 

In my car the GND wire on the wire harness adapter did not actually go to ground. I just wired the GND on the radio harness to a ground point I made myself. Try this, and if every thing is hunky dory, you should be fine.

 

Thanks, that's what I ended up doing. Works great now, but I'm not sure how it went wrong in the first place.