My trailer only requires the four prong plug as it needs no brakes or anything. Late last year some of my lights on the trailer quit working. Naturally I thought the problem was with the trailer but, as it turned out, it's the truck. I had forgotten about it until yesterday when I pulled the trailer out to unload it and get it ready to go back on the road. Brake lights, fine. one turn signal, sure. Anything else, forget it. I have an adapter to go onto the bigger plug which works just fine. I assume I am looking at a corroded plug on the truck and will check for that tonight if I get time. Could it be anything other than corrosion or perhaps a wire coming loose? Doesn't seem right for a 2016 Lariat but with all of the technology on these trucks, I felt I should ask before digging in too far. Not a huge deal since I can use the other plug but still, I would like everything to work correctly.

 

 

I got to get under the truck a little bit last night and see what's what. There is no corrosion in the outlet. In fact, it almost looks like new. So, I climbed under the truck and grabbed the harness and it didn't move even a little bit. Like I said, it looks like new under there. I noticed that the one harness takes care of both outlets so I imagine the problem is between the two. Having not pulled the harness out, I have no clue what's in there but I'm thinking I have a pretty good guess. I'll have to get more time to check into my theory. Thanks for the tip.