These do a great job of cleaning the connections and keeping the trailer lights working. Much cheaper than a ticket, or mechanic when it's simply a dirty connection.Here's a little trick. Sometimes the brass pins in the connector on the truck and trailer pinch together and make poor contact causing flickering, intermittent, or no function on that circuit. Use a small flat screwdriver, knife, etc to pry the two halves apart so there is an even gap to the base of the split. Give the connection a wiggle test with the lights on to see if they flicker.