Have you figured out the problem with your trailer lights? I hate dealing with electrical issues on vehicles but, have had to on so many that I have found that it is not as intimidating as it use to be. I have found that because your plug is usually open to the environment. corrosion can cause all kinds of issues. I would trace your wiring to where it plugs into your truck. They usually use a wiring kit. pull that plug to see if there is any corrosion in that plug also. I use a spray that cleans and neutralizes the corrosion after fixing the problem I would apply electoral grease in the positive holes of the wiring only. I do this to my old Jeep Cherokee XJ. In most of the electrical connections. So that the moisture from four wheeling won't get into those areas and cause all kinds of issues.