Front and rear camera hookup

I have a pioneer AVH head unit and I have the rear camera hooked up and working great with reverse. I want to add a front camera using a 3 position switch in the dash. I did a search and found Clarion Mikes write up but he has been a-wall for some time. I have everything he said he used in his setup but I don't see where the reverse input signal goes from the taillights or transmission (I have the taillight wire) Anybody done this and get it to work and can share some info on the wireing. Thanks

I have the rear camera all hooked up and working good. Put SS in reverse and camera comes on. I want to add a front camera that I can use a switch to activate when I am pulling straight into a parking spot so I don't hit the curb or parking barriers. I have everything that was listed by Clarion mike I just don't see where he connected the reverse trigger pick up from tail lights. He has the trigger wire from the radio going to the one side of the 3 position switch but does not show wire from the slingshot reverse lights going anywhere. Just don't want to wire something wrong and fry something

Tail lights are negative. I haven't even cut a wire yet. This weekends project, I have everything gathered and I am just preplaning for it. Right now there is no relay needed for one camera. I have it wired so when I put gearshift in reverse the camera comes on. I want a switch on dash to turn rear camera on while driving if switch is in down position and front camera to come on in up position and if in center position to activate with gear shift into reverse.