I have never heard or seen this before however I have an Anderson plug which is failing. I have followed the current and amps from my solar panels through the solar controller and the watt meter to the Anderson plug which goes into my camper however when I plug in to the camper the watt meter does not pick up the watt's or any other information from the solar panels but does pick up the volts in the camper batteries. if I use a voltage meter to connect to the back of the Anderson plug from the camper the watt meter springs into life showing all the information it should. My only thought is that for some reason the Anderson plug on the trailer is faulty. Any ideas or has anyone else found simular issues, I plan to replace the Anderson plug to see if it rectifies the problem.
As Tony says - make sure that all four "pins" are fully home. If they are give them a good spray of contact cleaner and with a bit of rag and a small screw driver get all of the crud out. They can get a remarkable amount of dirt in them - they are in a pretty vulnerable position after all. Especially the one on the vehicle when you're not towing.
