Anyone who tows a boat trailer often enough either has, or will, experience problems with the trailer’s lights. Either one turn signal doesn’t work, the brake lights don’t work, they work intermittently, or they show no signs of life at all. A number of factors could be the culprit, and more often than not, one specific culprit is to blame.

Checking the bulbs and the wiring is definitely the place to start. Corrosion is common in both areas, and blown-out bulbs are a fact of life. It’s always a good feeling to find and correct those problems, because you know what went wrong, and you know they are now fixed. But all too often, the lights just start working while you’re in the middle of troubleshooting, and while that makes you happy, you know the problem isn’t fixed. Worse yet, you don’t even know what the problem is, or how to fix it.

According to John Long, who runs South Carolina’s East Columbia Sports Shop, the mos-common cause of boat-trailer lighting problems is in the grounding of the trailer. 

“Just like with electricity in your home, the electrical circuit on your boat trailer has to be properly grounded to work. No matter what problem you’re having — whether the lights don’t work at all, half of them work, they all work at times but not at others — the most common cause is a lack of grounding,” said Long.

Long said even when the ground wires are hooked up properly and in good shape, grounding is still the first thing he looks at when someone complains their lights aren’t working.

“The trailer’s coupler touching the ball is what grounds the trailer’s lighting circuit, and this is where most problems lie. Rust on the hitch ball, rust inside the trailer coupler, paint on the hitch ball, or just caked on dirt — these are all common problems that interfere with the grounding process,” said Long, who advises boaters to sand the hitch ball with sandpaper or a wire brush ­— that usually does the trick — but sometimes it’s simply a matter of washing off layers of dirt.

“In most everything to do with a boat or vehicle, the last thing you want is metal touching metal, but for keeping your trailer wiring grounded, that is what you’ve got to have. Rust and dirt creates a buffer between hitch and coupler. Get that metal touching metal, and you’ll usually solve most trailer lighting problems,” he said.