Trailer wiring isn’t all that complicated, but most of us don’t have electrical engineering degrees, either. Sadly, most wiring problems are the result of a cascading series of events that can have you tearing your hair out, especially if it’s 4 a.m. and the scheduled departure is in five minutes. Some wiring issues are easy to diagnose, such as a broken wire, and that’s a good example of a problem that can start small and get bigger. A broken wire is easy to fix, but you can be setting yourself up for more problems. Let’s say you find a broken wire, which could have been caused by age, brittleness, chafe or someone simply breaking it. Easy repair, you think, grabbing a plastic box of pinch-wire connectors that cost a few bucks at Radio Shack. Big, big mistake, even though some trailer brands use pinch connectors, which cut through the insulation to join wires.
Pinch connectors are fine for fresh water, but salt water migrates into the cut and corrodes everything. When you have a lighting problem, you’ll look at what seems to be a good connector, never guessing that it’s your problem. For salt water, and really for all connections, use crimp connectors protected with heat-shrink tubing to eliminate future corrosion failures.
Let’s take a look at some other actions you can take that will keep everything lit and turn you into an electrical engineering whiz.
Don’t patch. Replace. When trailer wiring begins to have problems, your trailer is telling you it’s time to replace the entire wiring system. That may seem a monumental task, but it’s actually easy, as long as you have the correct new wiring harness and a notebook to take copious notes about where wires go. One experienced harness replacer simply snips off the old wiring harness, leaving two- to four-inch lengths protruding from the various lights and connections. That way, he just has to match up the colors, make the connections and be finished.
Get the correct wire. If you buy a ready-made wiring harness as a replacement, you won’t have to worry about wire size. But if you plan to make this a DIY project, or if you’re just replacing a few sections of trailer wiring, be sure you get the right AWG (American Wire Gauge) spools of wire.
Electrical wire is like a water pipe: too small and the electricity/water won’t flow. If you’re replacing factory-made wiring, match the wiring size, which is usually 12, 14 or 16 AWG, but that depends on the length of the wiring run and the loads on it.
A word about tinned wiring. It’s been said that tinned marine-grade wiring is absolutely, positively the only wire to use. It’s true that tinned wire adds a level of protection against corrosion, but it is not required on boats by either the Coast Guard or the American Boat & Yacht Council. In fact — some manufacturers prefer not to make this known — untinned wire that has been properly protected from moisture intrusion will last just as long as tinned wire. I use tinned wire on my boats and my trailers, because I never completely trust connections to be waterproof, and tinned wire gives me an extra level of protection.
Use the right connectors. Here’s where you may need advice from your boat dealership. Trailer plugs, which link your car to your trailer, once came in a fairly standard flat-four connector. Today, however, there are fours, fives, sixes and nines. And round connectors, to further muddy the waters. In addition, foreign and domestic cars require different systems and connectors, and trailers with disc brakes may need a separate wire to deactivate the surge actuator in reverse. Then, you have to protect all those black boxes and computers in modern cars, too. Best advice: See your boat dealer.
Carry a spare flasher unit. Most standard flashers aren’t powerful enough to operate more than your car lights, which makes your trailer tail- and brake lights so dim as to be invisible. Before you tear everything apart looking for a short, reach under the dash and replace the flasher with a heavy-duty flasher. It might solve the problem.
Last, let me repeat myself: Don’t try to patch and fix your trailer wiring system. You’ll fix one problem before another crops up. Better to bite the bullet and replace the entire wiring harness, making sure it’s properly connected and protected from chafe and corrosion. Sadly, that is the voice of experience speaking.
Don’t scrimp on grommets. Every opening in the trailer frame a wire passes through must have a rubber grommet to protect the wires from chafe. Trailer owners make two common mistakes here. First, they allow the grommet to age until it becomes brittle, pieces fall off and the wires chafe. Test each grommet by feel, and you’ll quickly see which ones have lost their elasticity. The second problem comes when you replace the grommets, which come by the box at marine or auto parts stores. Before you buy, know the thickness of your trailer’s metal. If you install a grommet with a half-inch groove around it onto quarter-inch metal, it will rattle around and fall out, leaving the wires unprotected.
Have the proper clips. If you have a trailer built with a C- or I-beam frame, always keep a handful of galvanized wire clips in the toolbox. These flat S-shaped clips slide snugly onto a trailer frame, and wires can be slipped into the clip to keep them from dragging on the ground or chafing in the wind. The clips seem to disappear on their own, so plan to replace one or two every time you check your trailer.