[Dirt4dinner]

I have a standard 4 pin Flat light plug I installed on my 4Runner. I have noticed since the day I installed it, that I either have brake lights OR trail lights, I can't have both. I just bought a vintage pop-up camper last night, and I need to get this problem figured out.

If the lights on the truck are turned on, then the tail lights on the trailer are on, but there are no brake lights.

If the lights on the truck are off (which is really never), then I have brake lights, but no tail lights on the trailer.

From what I can tell, the same bulb is for both the brakes and the tail lights on the 4runner, which means that it doesn't translate to the trailer very well, since it's just one wire that does both.

Help.

[Dirt4dinner]

Nobody has a 4 Pin flat trailer light plug on their 4Runner?

[broke down]

I just went through problems with my 4 pin. Traced the issue back to the factory "converter box" located near the passenger side tail light assembly, behind the plastic panel that covers the entire p.s. rear cargo area. The box had input voltage, but no output voltage. A little different from what you have, but may be the same part that's giving you traouble. I called the local dealer, and they wanted ONE HUNDRED AND SEVENTY DOLLARS for the part, assuming we were both correct about what I needed. I then went to a trailer/rv dealer and picked up a common aftermarket brand, sorry don't remember brand name, for twenty-three dollars. Fixed. Works great now. Do you have access/knowledge of a multimeter usage? That's how I found the source. If not take it to a respectable trailer service center. They should be able to find the problem fast. Another thing, with the muddy grimy location of the harness wires, I would demand soldering the connections together, don't use butt connectors, or scotch locks. It will be trouble free for a very long time that way. You do not want to get 500 miles from home only to discover that you have no lights on your trailer.