This is more applicable towards 2008+ Interstate Models although AS wiring may be similar.
I decided to add another radio/DVD/MP3/monitor in the single DIN spot above the Sprinter front interior lights but powered by the house batteries with use of the inverter. I was going to access the 12V
outlet in the overhead storage compartment but found an extra set of unused power leads in the wiring bundle above the drivers head once I had the panel removed. The only thing about the wiring was the color, (Black +, White -), which you should check anyway.
In any case, if you need switched house power with 10g leads upfront, it may be up there already.