Winter truck
You might want to start pulling fuses and see which one kills the tail lights. It supposed to be the fuse labelled tail lights but if you have a short to something else, it'll be another one. If the tail light fuse makes the lights go out, then I would suspect a bad switch somewhere. These types of problems are REALLY tough to solve. You'll have to get your voltmeter and start ruling some things out.
Or... just disconnect the battery when you park.

