My tailgate switch stopped working. Opened everything up and decided to replace the key switch.
Here's the GM Part # for the key switch. It comes with two pre-cut keys to operate the switch.
The existing key switch was a little gunked up, but didn't look broken.
Ultimately, I'm an idiot. This electric tailgate setup was retrofitted in the 90s. Once I replaced the key switch, it still didn't work. I followed the power wire directly to the power junction on the right front fender where a 30 amp fuse was blown. Always check your fuses, idiot. That said, the replaced tailgate switch didn't have a proper rubber seal to keep the water out. Perhaps the switch was shorting due to water and that burned the fuse. I've cleaned the replaced switch, and I'm gonna re-key the tumblers to the new key as a handy spare. I've also made sure I have the proper spare 30 amp fuse in the glove box.
As a note, I was able to pull the whole guts out of the tailgate without removing the glass by propping it up while rolled out and just removing 4 bolts for the window glass cam channel and the 4 bolts for the window regulator assembly. It really is an easy thing to work on.
Of course, I have removed the safety switch, but you can bypass that by hooking a cordless drill to the drive for the window regulator.