MICTUNING 4 and 7 Pin Trailer Plug Tester, Multi-Function7 Way Blade & 4 Pin Flat Trailer Light Circuit Tester with 6 LED Indicators for RV Truck Trailer Socket Tester. 2 in 1 Trailer Light Tester - Combines both 4 way circuit tester and 7 way trailer light tester, it's able to test both 4-pin and 7-pin connectors.