It's a Wednesday morning and Dustin Hoover of Legendary Trailer Repairs, outside of Annapolis, Md., is flat on his back beneath a single-axle Cox boat trailer parked with a boat on top in a driveway.

While this particular job doesn't involve helping a boater with a trailer malfunction along the side of the road, it's just as important.

"Trailer lights aren't working," he says from somewhere below the boat. "It's usually a bad ground or a bad connection or a bad bulb."

He crawls out from beneath the frame, his baseball cap remaining in place, stands and looks at the trailer. "In this case, it's all of the above."

Sunlight can deteriorate the seal around lights so if it's starting to look worn, replace it.A BAD GROUND

Like all wiring, trailer boat lights require a ground wire so that a light circuit can operate in an unbroken circle. Power goes from the battery (positive post), to the light, then back to the negative side of the battery, which is a ground (the trailer frame is usually a ground too, connected to the battery negative post). If there is no ground connection, there is no circuit and no light. If the ground is spotty, the lights may flicker as the connection is made and broken.

Consider the life of a boat trailer: it is pulled across miles of roadways – paved, gravel and dirt – and then it is submerged into water. That's tough enough on a trailer frame and it's more lethal for bulbs and the assorted wires connecting them. The bottom line is that it is no surprise that trailer lights have occasional trouble.

"Look for the white wire," Hoover says. "That's the ground 95 percent of the time. And the first place to check is at the connector on the trailer tongue where it ‘connects’ with the tow vehicle. It can be five-way flat or a four-way flat or a six-way round or any combination of connections. Pull it apart. Sometimes you're going to see corrosion where the ground isn't making contact to complete the circuit or it could be something like spider webs or dirt if the connectors have been unplugged between the trailer and tow vehicle."

Corrosion can be removed by sanding the area, but Hoover advises it may be easier to simply replace the connector altogether (the cost runs from $5 to $6). Hoover also recommends adding some dielectric grease to the connectors as a corrosion deterrent.

Check if the nut and bolt are loose or rusted, the source of a bad connection.Some trailer wiring designs attach the ground to the actuator instead of the frame. Hoover sees this often and the result is usually a trailer light problem.

"The ground on an actuator means the circuit has to go through more connections – the metal of the actuator and then through the bolts that hold the actuator – before it touches the frame. I always put the ground firmly on the trailer frame. That makes for a secure circuit and less is going to go wrong. It's a simple matter of cleaning the frame surface, drilling a hole, putting the bolt through the ground wire ring and tightening."

Every bulb, be it an incandescent or the newer and brighter LED, requires a secure ground too. But some lights won't be grounded with the usual white wire; instead they use the mounting bolt that holds the backing plate onto the frame. Check if the nut and bolt are loose or rusted, a common source of a bad connection. LED lights usually use a harness (all the wires are inside) but the mounting bolt should be part of the inspection if a light isn't working.

Remember, too, the stainless-steel or chrome hitch ball on the tow vehicle can also act as a ground – but it was never intended as such, despite some trailer boaters who maintain this is all one needs. It isn't. But the hitch ball can also provide a ground when a ground wire fails in the circuit, and that can make an inspection more confusing. Still, one should clean any rust, dirt and/or grease from the ball to ensure there's a clean connection.

A BAD CONNECTION

Wires are bent every which way on a boat trailer frame. Though they're covered and sealed in protective plastic and, in some systems, have corrugated tubing or a harness around the wires, wear and tear eventually wins. And as noted, a boat trailer by its nature is subject to constant banging and bumping on the road and then immersion in water at the boat ramp. After a while, the protection eventually gives in to wear and tear.

"I look at anyplace the wires make a turn," Hoover notes, and as he says it, he holds a wire that has been stripped to bare metal from rubbing against the trailer frame. "This is going to cause a bad connection and requires either a solid wrap of electrical tape or, if the wire is damaged, a replacement."

It's important to inspect all wires leading into the bulb assembly on the trailer. In fact, anyone who works on boat trailers will tell you it is essential to take 10 minutes and check connections for not only bare or loose wires, but evidence of corrosion where the wires actually connect to the bulb assembly, backing plate or bolts holding the light on the trailer frame. Hoover sees it this way: vibration on a boat trailer is common as are wires and bulbs. The constant movement is eventually going to affect connections between the two.

The stainless-steel or chrome hitch ball on the tow vehicle can act as a ground – but it was never intended to be used that way. Now Hoover is pointing to a rusted bolt holding a light on the trailer frame. "You can see the corrosion on the bolt," he says, "and that tells me the rust is getting between where the white ground wire is located and the metal surface of the bolt. This means there's no voltage flowing through."

He replaces the bolt, adds a new contact for the ground and secures both to the frame. Then he brushes some liquid electrical tape (made by Star-brite) onto the new connection. Another option is to apply an electrical contact spray (there are any number of manufacturers available; CRC Heavy Duty and CorrosionX are two popular brands used by trailer boaters) which is useful if you're on the road and need to make a quick fix to get home. Simply spray it on and wipe the residue off with a rag, which cleans the surface.

A BAD BULB

This is the simplest of all trailer light troubleshooting. If a single light isn't operating, remove it and test the bulb in a similar light socket that you know is working. If it lights, then inspect the connections and ground on the suspected bulb assembly. You can also check the socket with a 12-volt test light (this is a good investment for checking voltage in wires).

Incandescent lights have a filament and if it's damaged, you'll see it right away. LED (light emitting diodes) lights use electrons flowing through a semiconductor material, which results in a brighter and cooler light that usually has a longer life than incandescent bulbs. If an LED light isn't working, it's time to replace it.

Make a point of inspecting the rubber grommet that houses the trailer lights. Sunlight can deteriorate the integrity of the seal around the lights so if it's starting to look worn, replace it.

After half an hour of work, Dustin connects a battery to the trailer lights, walks around the trailer and with a smile, pronounces every bulb is burning brightly. He packs up the tools and equipment, stowing it all in the back of his van and checks email and takes a phone call.

"Lunch will have to wait," he says, "I got a trailer in a yard 10 miles from here . . . no lights." A minute later, the van is on the road and chances are good when he stops, there'll be a bad ground, connection or bulb waiting for him.