Trailer connectors have been the bane of my existence for about 40 years.
Drive through water, corrosion will begin. The cheaper the plug the worse it gets. Intermittent electrical problems. Lovely. Hard to track down. Brakes that maybe work sometimes.
I've been using solder and heat shrink tubing for 25 years but even using electrical grease, the connectors are just not well made for the environment they are used in. Even tried the big plugs from semi-trailers. Same deal eventually.
The plug and connector are the single largest service problem of any trailer. They never quit working completely, just kind of. When you finally have to work on it, its never in a flat parking lot in 70 degree sunny weather. Its usually either below zero and dark or hot, muggy, and raining like hell. And then the spot that I've got to work on the thing is in the lowest part of the lot. Usually covered in water, mud, or a snow bank. Murphy invented the trailer connector I'm sure.
Last year I found this connector. It is sealed and magnetic. I have never seen anything of this quality anywhere. I've been beating the tar out of it and it is still working great.
Worth every penney. The brakes work right every time. Martyn and Mario should consider making this standard equipment on their line of trailers (if they don't already use it).
http://www.ezconnector.com/ezstory.html