OK, took everything apart and have much more info.
The monitor cable passes over the driver's door, and down the pillar behind the driver's door. If you remove the pillar trim , the cable ends in a cluster of wires. It has a red wire and a black wire, which pass through a small black box with a fuse and filter circuitry, then tie in to the 12v system. These red and black wires also connect to the cable which runs to the camera at the rear. A blue wire has been cut off. There is a yellow RCA connector which is unused, and a white RCA connector which connects to an RCA connector which goes to the camera through the floor, inside a corrugated black plastic conduit, along with the red and black power. If you remove the camera at the rear, remove the grommet that the cable passes through, and pull out the caulk, you will find a four pin connector.
I took my camcorder, plugged the output into the white RCA connector, and confirmed that my monitor works. Then rigged a wire to the RCA connector, and connected the bare video wire to the yellow wire that had connected the camera. When that worked, I knew that the cabling was good.
That leaves the camera. I will post again when I have obtained a replacement.