I always tense up a bit when I plug my trailer lights/brakes into the truck, and say a small prayer that everything comes on as expected. I’ve found that even though the trailer is under shelter and the plug is protected, sometimes tiny bugs get into the plug’s holes and prevent a good connection. The best cleaner I’ve found is actually from the baking section of the store–those tiny brushes used to clean out frosting from the decorating tips. I found my brushes at the local Michael’s store. While they’re a little pricy, I waited until I had a 50% off coupon. I also put one of those cute little jewelry bags over the plug when not in use–it doesn’t allow moisture to build up as a plastic bag might, but keeps a lot of bugs and trash out. If you don’t have any lying around the house, the bags also can be purchased at the local craft store. And remember: check your lights and brakes before every trip!