There’s a bundle of wires in the floor panel running on the drivers side door. Can anyone tell me which is the accessory? Or the easiest place to tap the accessory?
Thanks!
It’s that one! … No the other one. 
Seriously though, if you want to find an accessory wire, the easiest is probably to use the one going to your cigarette lighter. Failing that you need to use a test light or a multimeter with pin probes so you can check for power in the various wires.
Welcome to the forum BTW. 
Yes, both of those options work… but with the plethora of Tundras with train horns, I figured someone might know so that I don’t have to go through the trouble :\
I’d try Tundra forums.
I had a Tundra, believe it was a 2008? Hell I can’t recall. I pulled switched 12V from the trailer hitch harness.