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.

According to Phillips Industries, the December edition of its monthly Qwik Tech Tips newsletter outlines “in clear language” how best to troubleshoot trailer lights when they are not working properly.

With fishing seasons nearing, now is the time to give some thought to the most common problems related to boat trailers: lights and wheel bearings. LIGHTS: The most common headache with boat trailers ...