1a auto suggest installing the switch in the little cubby by your left knee where the factory brake controller is. Some people have that some don't. You could install it by the switch but you will have to cut the harness it comes with and splice in more wiring to add it longer and then it will work. That's what I did. You also have to tap an ignition on power source (25a) if i remember right. I think i tapped my factory fuel pump fuse as I have a fass and its not connected or used anymore.
The hardest part of the whole install was making the cuts in the door panel and switch and feeding the wiring through the rubber tubing at the doors. I suggest long ass zip ties and electrical tape to help feed. or a metal coat hanger with rounded tips so you don't snag or poke anything with the sharp end. all in all took me 4hrs to fully install. 2hrs to decide where to mount.