I started this thread because I can't enclose an attachment in a personal message.

The grey wire is part of the illumination circuit, it's function is to power the radio's backlighting (the orange lights that illuminate the radio's ***** & such) . The grey wire is fed from same variable voltage source coming from the dimmer circuit that powers the dashboard lighting, this way the radio's backlighting will dim with the dashboard when the dimmer wheel is turned. The brown wire is a separate source from the illumination circuit that activates the radio's display dimming function when the headlight/running light switch is turned on. This wire is the one that dims the radio (and clock) numerical display. This wire is not variable, it's either +12V or not, depending on the lightswitch.

The reason you'd see +12v between the orange & brown wires is because with the lightswitch off, the running (parking) light bulbs are a path to ground for your meter. You'll find that if you turned the running lights on, no voltage will be seen between those two wires (since at that point both would be at +12V)

I hope this helps, here's a diagram showing the radio's different power sources (4 in total, the Orange, Yellow, Grey, and Brown wires)

 

Wow, thanks! You totally explained it and it makes sense!...

 

Your welcome