5 Wire 4 Prong Trailer Connector. Trailer connectors are used for connecting vehicle wiring to trailer wiring. You've connected the trailer to the vehicle, but the turn signals and brake lights don't work.
The three prongs are for the two "hot" leads and the third is for the equipment grounding conductor. One way to troubleshoot the voltage on the connector plug is to use a circuit tester. Connect one end of the spare piece to the other marker light wire, using another butt connector.
Fifth wire is hooked up to back-up lights circuit to disengage trailer brakes when reversing.
Here's a rundown of the common types of connectors and how they So, imagine a four-pin trailer wiring connector as if it's simply a household plug with four prongs.
Usually, the connection involves inserting the bare wire into the neutral slot, then securing it by tightening a screw. Used on marine trailers with surge couplers. This T is made to fit between your wire connection!