I have seen a lot of threads on here concerning trailer light issues with the factory converter and harness. I had the same problem in my Double cab 02 tacoma. Inconsistent lights are the issue. The converter is located behind the left rear seat of my tacoma. I tried taking the cover off to troubleshoot and broke the clips in the process. I had dc on some pins and none on others then i started pulling on the wires that go down behind the panel that the converter is mounted on and noticed that there are fuses (5A) behind that panel. Some were blown and some were not (explains inconsistency). I have not seen anyone else say anything about these fuses so I just thought I would post this thread to help anyone in the future who might have this problem. If some of your lights work and some dont on a 4-pin trailer then this will most likely be your problem.