Trailer Light Wiring Adapter 4-Way Round Vehicle Side to 4-Pin Flat This wiring adapter is designed to a convert 4-pole round pin vehicle connector to a 4-way flat trailer connector. It's the fastest and easiest way to make electrical connections when pulling a trailer that has a different wiring configuration than the vehicle. The rugged construction will offer years of trouble-free service and the compact design allows for convenient storage when not in being use to pull a trailer.