Anyone have experience with a rearview mirror backup camera set up?

[Rich69shortfleet]

How do trucks with the roof mounted exterior running lights get the wiring down to the electrical system? And how were the wires run up to the top front of the cab? I assume the wires ran between the inner and outer skins of the roof, but how were the wires installed in the first place?

Edit: I did some searching and also reviewed the assembly manual and if I wanted to run the wiring through the cab roof it seems it would make most sense to run the wire from the mirror location back to the dome light location and then have the wiring follow the dome light routing.