Our only problem on the recent trip to the national parks was caused by a bad light. The 7 pin harness plug was the actual culprit, but I went under the trailer in more than 90 degree weather to not find it. I wiggled & tugged on every connection I had made, but no luck. Long story short, use di-electric grease on your terminal ends when making a harness connection. A very small amount of grease is all that's needed to keep things working well.
We went through a hard rain storm on the way from Tucson to Flagstaff on the first day out. The next day the left turn signal & 3rd brake light stopped working. The pin for that one is at the 6:00 position on the plug & it's more common than I had imagined. Water collects at this low point in the plug & causes corrosion which will then cause an intermittent connection. I helped two other people with their trailers cure the same problem shortly after our problem was solved. They all said the same thing "our left turn signal won't work and..."
NAPA sells a tube of grease for a few dollars which will last you a lifetime, so do yourself a favor, use it & all will be well.