Shop Nilight 4 Way Flat Trailer Wiring Circuit Tester Male End Wire 4 Pin Test with Bright Light Indicator for Turn Signal Brake Tail Lights Trouble Shooting in high quality, support 2 year warranty. 4 pin trailer socket tester is made from durable ABS plastic. Designed to be weather, corrosion, and impact resistant for years of reliable service. Tin-Plated copper terminals makes great conductivity.