you can go new 12vdc cam to old deck 6vdc, new cam 12vdc to new deck 12vdc , old cam 6vdc to new deck 12vdc,
the quality of the stock cam 2006 on a new screen is good, in my case it was. (pioneer)
the quality of a new pioneer cam was only slightly better than the stock picture on a new screen. (pioneer)
I don't know if the quality of the picture would be beneficial with new cam on the old screen
a new cam 12vdc on a old screen that didn't have a cam installed from the factory might be problematic, obviously you don't have a television ecu to molest. Any input that could be used would have to be exploited by after market stuff, maybe like the post above mine. I don't know.
Any car that cam with a cam can just be wired as you like keeping track of voltages. I've had old cam to old screen, old cam to new screen, new cam to new screen.
My transistor failed, that was the reason to install a new cam for me. But the camera never failed itself.
Looking back now I probably should have just installed a new cam, 12vdc in the first place. I was probably tired of wiring at the time.
Installing a new cam on the spare tire mount (see
@WickedPickle ) is easier than moving the old one. Just know that new cam with old deck needs a transistor and getting to the ecu under the seat at the very bottom of the pan. A new cam with new deck you could ignore the television ecu and run all new wire from back to front under the truck penetrating close to the seat pan area passenger side, best option in my book.
IF someone with a rear carrier wanted a new cam mounted anywhere on the carrier to the old screen I'd go the way of wickedpickle as far as routing goes, under the car to the seat pan. Transistor mount under the pass seat to television ecu.
same instance if a new stereo, rear carrier mount, under the car to passenger seat area the up to new deck.
without a rear carrier but with a new cam it makes sense to go through the hatch under the inside upper trim, down the passenger side, down rear passenger door carpet, under to the passenger seat pan. then onto a new deck, or stock ecu.
integrating the newer cars television ecu into an old car that didn't have one would be difficult. There is a guy on here that tried and couldn't get it going. In those cases it would make sense to just get another screen and mount your cam wherever you wanted it, using a complete kit, screen +wire+cam, hard drive to record, etc etc.
there's info on the 4 runner forums about transistors and stuff.