[jcp123]

You would want to do it two ways: wire it to your fuel injectors, and another switch to your torque converter lockup. Engage lockup first! Then cut off injectors. You maintain power to your accessories and the locked up converter still allows your transmission's fluid to be pumped, keeping you from trashing the transmission in a month or two. The two-switch setup is the best I can think of unless someone can think of a better setup for a GM full-size FWD.