How to Get the Juice Flowing Again

The first rule in trailer-light diagnostics is this: start with the easiest and cheapest solution. The most common diagnostic mistake is assuming that the problem is huge-before checking for the basic garden-variety problems that have always hounded electrical systems and always will. Fact is, you’ll rarely need to do much rewiring.

Start by asking the driver (or yourself) exactly what the lights are doing. Are they affected by bumps in the road? Do the lights work sometimes and not others? When was the problem first noticed? Does rain have any effect?

The answers should narrow things down a little bit. By now you should know which lights and circuits are suspect. The next step is to look at root causes, and that, too, is a relatively simple process. Any shorts you may discover are directly related to one or more of these items: corrosion; loose or broken wires or connections; physical damage to light fixtures; and light cord or receptacle failures.

THE RUST DEMON

Corrosion creeps in and rots connections. It causes a significant increase in electrical resistance (measured in ohms) which in turn places an increasingly heavy load on the entire system. Wires get warm and sometimes the circuit simply quits.

Look for corrosion in splices and crimped connectors, especially those exposed to the elements. Corrosion can even grow inside insulated wires, especially if there’s a break in the insulation or an unprotected splice or connection. Inside wires, it appears as a powdery green crud.

This is why you shouldn’t use a “bug light” tester to prick a wire and check for “juice.” The spot where you pricked the wire is an open invitation to failure caused by corrosion. The bug light is acceptable for testing continuity at exposed connections where no damage can be done, but nowhere else.

Unsealed canister-type tail-light fixtures are especially prone to corrosion. Old age, corrosive chemical agents, and moisture are the culprits. Look inside all junction boxes, even those that are supposedly “sealed.”

LOOSENESS

Looseness can pop up anywhere. Sometimes wires pull out of crimped connectors. Sometimes screws and nuts work loose. Marker light wires are especially vulnerable to being dragged off by limbs and brush. Any of these will result in intermittent connections and/or shorts.

As with all electrical diagnostics, begin by eyeballing everything. When something looks odd, check it out. Check the receptacle on the nose and the rear, any junction boxes along the way, and the connections for each light fixture. Double-check any dangling wires, then secure them.

Don’t forget to check for proper grounding, an absolute requirement for any electrical device to function. Some fixtures ground through the mounting screws while others have a separate ground lead. Check all the possibilities.

When checking for looseness, use your fingers to do a wiggle test. Once you’ve figured out which circuit is in trouble, turn those lights on. Start by wiggling the light cord plugs, then work your way along, wiggling the wires and watching what happens. When wiggling something causes the lights to blink or makes sparks fly, you’re on top of the problem.

Soldered joints can also work loose. Open up the light cord receptacle and check the pins. If the pins wiggle easily, there could be a loose connection. Replace that portion of the receptacle, and check all the wires and terminals attached to it.

LIGHT CORDS

Light cords are doubly vulnerable to problems, including loose connections and corrosion. They’re plugged and unplugged, then yanked and snatched. They get splattered with dirt. The most common light cord problems are loose screws, dirt, crud, and broken wires, but diagnosis is fairly simple. Turn off the lights and remove the light cord from the tractor.

First, clean the holes in the plugs. If a plug is full of grease from the fifth wheel, you can clean it with a shot of starting fluid (turn off all the lights and don’t smoke when you do this).

Then, take a close look at the plugs and the entire cable. Check for damage caused by the cord rubbing against a hot exhaust pipe. Has the cord lain against the edge of the frame rail or deck plate and chafed? Does the plug show signs of severe wear and stress? Are all the parts there, including the spring and the clamp?

Take the plug apart and look inside. The little screws commonly work loose, and wires can also break just behind the screws. The screws can fall out and short an entire circuit or two.

The retaining clamp on the plug can also cause grief. When it’s loose or missing, the little wires get jerked loose. When it’s too tight, it breaks the wires. Torque it enough to hold the cable securely, then quit. Be sure it clamps against the heavy outer insulation and not directly against the internal wires.

A cord can also have internal breaks in the wires. If you don’t spot this visually because of a lump or depression in the surface of the cord, you’ll have to confirm it with a voltmeter after you’re sure the plugs are OK. This kind of damage often happens when the cord becomes entangled in the air lines, then gets snatched when jackknifing to dock the trailer.

Light cords can often be repaired by cutting off a few inches and installing a new plug. But make certain that you don’t allow any stray strands of wire to frazzle and create a new short. If possible, solder the wire tips before installing the new plug. When you clip the cord and trim back its heavy insulation, be cautious not to cut into the insulation around the smaller wires, which invites corrosion and shorts. Seal the screws with a dab of fingernail polish to keep them from working loose.

PREVENTION

Many trailer electrical problems can be prevented, starting with proper spec’ing. Buy heavy-duty light cords with at least a 10-gauge ground lead and 12-gauge for the other six wires. Spec sealed wiring harnesses, of course. Conceal all wiring in plastic conduit if you can; otherwise, keep it carefully tucked out of harm’s way. Install light fixtures so that they are not easily knocked off.

Make the electrical system a regular part of your trailer PM program. Repair small defects before they become problems, preferably during the PM inspection to eliminate downtime later. The best emergency repair is the one you don’t have to do.