Features: 1. 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. Note: The trailer tester will upside down when testing for 2017 Newer Ford/GMC/Chevy model. Can't test LED lighting system. Doesn't work with vehicle has a lamp-out sensor, such as BMW, VW, Audi, Mercedes-Benz, Porsche etc 2. 7 Pin to 4 Pin Trailer Plug Adapter - 7 way trailer tester can be also used as a 7 way to 4 way trailer adapter, converts the vehicle-side 7 pin blade output to a 4 pin flat adapter 3. 6 Light Functions - This tester used to test 6 separate trailer light functions, testing taillights, reverse lights, turn signals, electric trailer brakes and 12V auxiliary power on your vehicle .