1999 Chevrolet Suburban C1500, Radio Wiring

Ok, short update: I drilled a ground hole in the frame and connected camera black to that. Also tapped into the fuse box and ran aux power to the back to power camera so that it is always powered. Now the one thing left to do is tap somewhere into the reverse light signal. Camera works and radio does, too. But have to manually switch to the camera. Input wire for reverse is connected to the radio and is coming out next to the RCA plug (little red wire on picture). Would the light green at the 4-flat plug work for that? I am scared to tap into that one. How hard would it be to install a new 4-flat plug in case of problems in the future?

Last update: tapped into the light green wire at the trailer harness (which is indeed the reverse signal) and connected that back to the reverse signal input of the radio. Everything working now.