Jim,
Awesome solution! This is exactly what I was hoping to find. I'll do a web search for the "add-a-circuit" to find a vendor. Fused power source, dedicated line. I have old '02 CLK convertible I decided to keep and want to do the same thing on that car also (mount my Garmin Zumo to the dash using a RAM ball mount near the center ventilation ducts).
Huge thanks! Jim