They have an adapter plug that will plug into your 7-way trailer connector and shorts out the proper two blade sockets to turn on all your trailer running lights. this will run down down your trailer battery if left on too long if you are not connected to shore power
TRAILER CABLE CONNECTOR BEFORE
TRAILER CABLE CONNECTOR AFTER
Or you can just do this yourself with a short piece of wire or use a regular CAR FLASHER to plug into the two connectors and the trailer running lights will flash... Your camping neighbors will just love you to death doing this...
Not really TOO TECHNICAL... Notice the raised FLAT area on the plug just above the pins 3 and 4. This is the key to look for to identify where the pins 3 and 4 are located.
Photos from Google Images