[RC-Monster Mike]

You could wire in a switch, but I wouldn't bother. It will only add a little resistance. I recommend that you test each system seperately (not driving, but check for operation) on the truck and program the controllers seperately as well. You must make sure both controller/motor combos are on the same settings and turning in the right direction. After you are satisfied that both systems are working properly, you can then wire them in parallel to your receiver and test again to make sure both systems are still working (take off pinions or move away from spur gear to test). It is important to check things out at each step to avoid costly mistakes.