Vehicle Trailer Wiring 7-Way Circuit Tester with 6 Function LED Indicators Essential safety tool for quick checking of vehicle wiring configuration/status for towing Plug into 7-way vehicle trailer light outlet; LED indicator lights for 6 separate functions Left and right turn, tail, brake & marker lights, power to trailer, back-up/aux & electric brakes No batteries or wiring needed; compact size Fits all standard 7-pin wiring configurations