Hi. I recently bought a 99 4Runner ltd for my son. This is my 4th 4Runner. The passenger taillight does not work, tried changing bulbs even went to a junk yard and got a different harness because the old one was a little brittle. I assume its not a fuse because the brake and the drivers side work fine. I also noticed that the factory (at least I think that all the ltd's came with towing package) trailer wiring does not work. I have read were the little black box that converts the taillights for the trailer can go bad. I picked one of those up at the junk yard also but that didn't work either. actually it made the brake light not work. So im thinking that one was bad and maybe the one I have in the truck now is causing the taillight function to not work,. Is this possible or is the problem in the wiring?

 

Maybe bad stuff from the junk yard.
Pull out your multimeter and check for an open or short circuit.

 

Quite possible the converter box you got at the yard was also failed just like yours .

 

Yeah im sure that the junkyard box was bad, because both taillights didn't work with that box. When I put the old one back in it went back to the drivers side working and the passenger side not.