I have a very strange problem with the passenger side lights on my trailer, in that sometimes they work, sometimes they don't. I have a second truck that I hook up and it works every time. The real weird thing is I have a tester and when I hook it up to the problem vehicle it lights up for everything, and shows no problems. Most of the time when I first hook up the trailer it won't work, but if I then turn on the truck and re-attach the connector it starts working just fine. I thought the problem was with the truck, but the tester shows every function working every time. That means it must be in the trailer, but then why does it work with my other truck? It is a perplexing problem and it is driving me nuts. Does anyone have any ideas for me? I have tried re-grounding both the connections in the truck and on the trailer, and that hasn't helped. I changed the plug on the trailer side, and the plug in the truck is brand new as well. Is it possible that my battery in the truck is weak, and causing the problem with my brake light, and then when I start it and the alternator adds some juice it gets enough power to function? Any help would be greatly appreciated.