Side view cameras?

H2O_Doc

Thanks, I was hoping you'd post (and thanks to SouthArk370 as well). I only want one camera displayed at a time. Now, as my name would suggest, I know some stuff about fish and bugs and (literally) pond scum; what I don't know is car audio and electronics, so please bear with me:

Does the HU display video when a camera plugged into the rca video in receives power? E.g. the HU doesn't really know when you've put the car in reverse, it receives a signal because when the car is put in reverse the camera is powered on and the signal is transmitted?

If that IS the case my logic is simply to power one of two side cameras when the turn signals are on and have the power off when the turn signals are off. I'd have to have a 3 into one rca cable or box, but because I only want one signal at a time, it doesn't sound too complicated (at least to a biologist ignorant of such things).

SouthArk pointed to maybe needing an off or on delay relay as the power presumably pulses from the turn signal (unless the lights are like my Christmas tree).

Is any of this feasible in both an electronic and practical sense?