This is the primary cause of trailer-light problems. Symptoms include flickering, fast-blinking, dimness, intermittent operation (often when a trailer ball is used for a ground), and complete failure.
Ford is recalling millions of 2021–2026 model year trucks and SUVs over a trailer lighting and braking issue that could result in a loss of critical signals while towing.
Over 450,000 Chrysler, Ram, and Jeep Vehicles Recalled Over Trailer Brake Issues ...