I picked up a broken one from eBay for $25 shipped and got the wiring harness for testing. So far I am unable to find why it won't power up, everything is testing fine. I am able to get the blue ring to light up, and I think the white lights for the LCD. I removed the controls, and I am fairly certain I can solder new LEDs and change the color of the blue ring to green/yellow. It would be a single color change, not selectable. I am considering getting a functioning one and trying it out in my car. I currently have the Kenwood in mine, but want rear USB iPod support.

I am going to put new LEDs in this one I have, and if they look OK, I will swap the display to the new radio. And if all goes will, I will have spare parts to swap with other peoples if there is any desire for that. Changing the white LEDs for the LCD display may be more difficult, they look like they are covered and the LCD might need removed for access. BUT, a green film over them might work easier then soldering in new ones.

Also, if anyone has the M502, you can easily move the unused harness's to the interior to save room behind it on installation. All power/heat generating components are at the rear and that would actually help airflow and not harm anything inside. It is extremely empty inside the radio.