School bus camera video observation system wiring requires 3 power connections: Red to 12V constant, Black 12V negative or chassis ground,
Yellow/Blue: ignition-switched 12V power when the bus is running. Normally, this is a simple installation for the wiring.

Most school bus camera systems are powered from the driver-left electrical access panel or the outside electrical panel.

This is no different for most of the Warehouse Terminal 5th Wheel King Pin Trailer Swapping Yard Mule Camera applications that share the same truck tractor front cab electrical connections.
https://vehiclevideocameras.com/mobile-video-applications/cs1-spotter-5th-wheel-king

The same is true of the Head Start  Pre-K Pre-School Nursery School Child Safety Bus Camera Recorder systems we offer to help manage the high risk of those transporting the younger children.