Paul - by "pre-wired", are you saying there is a black plastic housing on the rear cap area for a camera? If so, that housing is likely by Furrion and it's designed in two ways to accept only the Furrion brand camera.
1. There's a cover that comes off that housing (4 tiny screws) and the Furrion camera fits into that space behind the camera
2. There's a power connector behind the cover and that connector mates up to a Furrion camera
Hard to say how it's powered. You may need to contact Heartland Customer Service on that (877-262-8032).
This all said, I have used that Furrion pre-wire with another brand of camera by:
1. Removed cover, drilled holes in it and mounted another camera to the cover
2. Hacked the power cord by removing the connector, exposing and using the power wires to connect to another camera.
So it is possible to use the Furrion camera pre-wire with some other brand of camera, but it's not designed for it and takes some cutting and drilling. The Furrion solution is plug-and-play.