This particular plug-in harness provides a 4-way flat connector socket and is designed to be a custom wiring harness to fit certain years of the Jeep Grand Cherokee and Jeep Grand Cherokee L (to verify your vehicle compatibility, see application info). Custom Wiring Harness, 4-Way Flat Output, Select Jeep Grand Cherokee, L A custom wiring harness -- also called a T-connector -- is a simple, plug-and-play electrical device that plugs into your automotive electric system and provides a standard, universal trailer wiring connection..