What is the function of pin 4 on a 7-way plug?

Pin 4 on a 7-way plug is designated for the power supply of identification, front, and intermediate marker lights on towable trailers. This pin supplies voltage to the running lights, ensuring that they are illuminated when the vehicle is in motion and providing visibility to others on the road. It is specifically designed to allow for proper signaling and identification of the trailer in accordance with road safety regulations.

Understanding this function is essential for anyone inspecting trailer chassis or electrical systems, as proper lighting is vital for compliance and safety on the road. Recognizing the role of each pin in the 7-way configuration helps ensure that all trailer functions are operational and that the connections are correct to avoid any electrical issues during operation.