I see your coach is built on a Workhorse chassis. Follow the links below.
Winnebago Wiring Diagrams
2007 Adventurer/Suncruiser G33V Wiring Diagram Book
Backup Monitor Installation
(Sheet 2 Zone D-8) (page 3 of the PDF)
Automotive Wiring Diagram
(Sheet 2 Zone D-6) (page 5 of the PDF)
Now looking for source of wire "LD"
Zone D-4 of same drawing, is on fuse E1 of the "WH I/P Convenience Center"
Where is that?
Front End Wiring Installation
(Sheet 3 Zone B-6) (page 4 of PDF)
Also shown in View CE Zone B-2 of same drawing
Fuse E1 is the third row from the top, farthest left.
Also helpful is the "secret decoder ring," a link off the first link above:
Wiring Identification Guide
I note that "LD" feeds other circuits, such as the power mirror relay, so those circuits should be dead, too, if fuse E1 is blown.
This is for a single-camera system. If your coach has a three-camera system, there is an additional two-wire connector to chase through the diagrams.