Wire identification for a camera system install
"yellow" is probably the center conductor of the coaxial cable for video, the black one beside it is likely the shield/outer conductor and grounded. Hard to see for sure with a mess of black goop on there.

A BNC coax has two conductors - a center conductor and a circular shield conductor around the outside.

Red is likely + DC (12 or 24 volts most likely) black will be - DC and probably also ground in most (not all)  systems.

If the current system is not running coax (which it obviously has in the "video part" picture) all the way to the cameras you might need to run new coax. If it does, but without connectors, you might need to crimp new connectors onto the coax.