I hate troubleshooting electrical stuff, but thought someone might have a quick answer to fix this problem. -Both tail lights come on when I turn on the lights. -Both brake lights come on when I push in the brake pedal. -But, when the lights are on and I push in the brake pedal, the passenger side tail light goes off. When I release the brake pedal the tail light comes back on.
only thing I can think of would be a bad ground/short some where. I know after upteen owners each doing their own wiring magic on my truck I am happy that it works like it should, though I really want to rewire the whole thing someday. here is the wiring diagram from my '81 FSM, it is pics, need to get it in PDF format someday but it might help you out: s119.photobucket.com/albums/o159/ocdropzone/81%20toyota%20truck%20wiring/
most likely , as Robb mentioned , a ground problem . I would start by plugging in a new/or different tail lamp assembly .. even the working side would work as a "test lamp" .. the trekkers have the goofy mounts , so i'm not sure if you'll even be able to get the tail lamp out ? maybe visually check the back of the housing for the connection of the ground points .. alot of time , because the housing is exposed , the bulb sockets are rusted .
I know this is a old thread, but this might help somebody one day, but i had huge problems with my rear lights, turned out on the passenger side behind the front seat is the main clip that runs all the back lights, mine had lots of water and mud in it and corroded it out, took it all apart rewired it and all works good again.