Trailer's got a Small Round plug, your car's got a Flat socket, and you're staring at two connectors that refuse to meet in the middle. This Jaycar lead is the bridge. 7 Pin Small Round socket on one end for the trailer's plug, 7 Pin Flat socket on the other for your vehicle. Roughly 20 cm of cable, no cutting, no soldering. You plug both ends in, check brake lights and indicators, and you're driving. If your setup needs a different pairing, the PA2061–PA2066 range has all six 7 Pin combinations covered. Just match the adaptor's plug end to your car's socket and the socket end to the trailer's plug. Done