Making a Start on Choosing a Trailer

This post was written by bradylord on September 30, 2012
Posted Under: Cargo Trailer,Utility Trailer

Recently I read that for every trailer sold in the United States, namely car hauler, cargo trailer, dump trailer, landscape trailer, models and the like, there are 4.3 wiring kits sold. That just goes to show that there’s one thing all RV trailers and utility trailers owners have in common: At some point, usually when it’s least desirable, their trailer lights will fail. So, while wheel bearing problems are the number one source of trailer problems, electrical problems definitely come in a close second. If you currently own a trailer, you probably already know that purchasing after-market trailer light kits is part and parcel of trailer ownership. Water is the natural enemy of every electrical connection. Trailer owners often joke that there is always water, lying in wait, just dying for a chance to corrode even the tiniest connector crimp. So, what’s the solution? Keeping water and electrical wiring as far apart as humanely possible.

Vigilance and consistent repairs can help fend off electrical problems for quite a while. Addressing grounding problems and broken wires as soon as they crop up can hold the enemy at bay. But, eventually you’ll have a lighting system comprised of more patches that original wiring. And, that’s when it’s time to replace the entire wiring system, lock, stock and barrel. Plan ahead, and you’ll have the luxury of replacing the system at your convenience. Keep ignoring it and you’ll probably be forced into a last minute overhaul, hours before shipping off on a long-planned, special trip.

RV Trailer Wiring Basics

Most cargo, dump, landscape and tow dolly trailers have three circuits. One is responsible for the running lights, while the other circuits run current to the left and right brake lights. So, you’ll need 3 wires for these three circuits, plus, your ground wire. This means you’ll need a connector with at least 4 contacts.

Much as you’d expect, a standard, flat style trailer’s electrical connector utilizes 4 pins. The ground wire’s male pin is enshrouded and found on the vehicle end of the connector. Scrutinize a variety of 4-way connectors and you’ll see, they come with 4 color coded wire leads (White, Brown, Yellow & Green.) that do the following: A. The white lead wire is the ground wire. B. The brown lead wires, which exit through one pin and extend from the flat connectors, feed current to the running lights. They split power to the trailer’s left & right sides as well as the tail, license plate and clearance lights. C. Next comes the yellow wire, the primary power feed for the taillight’s left turning and stop functionality. D. Finally, there’s the green wire, which is responsible for the current running to the taillight’s right turning and stop functionality.

To determine a trailer’s right and left side, always stand at the trailer’s rear. Once you’re there, if you find a five way flat with a blue wire, you’re looking at your back-up light’s power source. This activates the back-up solenoid on disc brake equipped trailers (Now considered standard practice.) Understand that this 5 way connector and blue wire is utilized in trailers equipped with electric brakes; heavy duty trailer models, landscape trailers and dump trailer models being perfect examples. It’s also commonly used with trailers that sport back-up lights.

In doing this kind of maintenance, you’re going to come across connectors featuring six & seven way round connectors with round pin, blade or oblong terminals. The seven-way round blade style is the most popular, being favored for factory tow packages by the major, tow vehicle manufacturers. Be it landscape trailer, dump trailer or cargo trailer, roughly 90% of these kinds of trailers sport the seven way round, RV Blade style connector.

Most tow dolly and heavy duty trailer models have electric brakes and other 12-volt needs.  The sixth pin can supply power to interior lighting and other power needs inside the trailer. On 6 and 7-way round connectors, the wire color code should be the same for the Trailer’s running, stopping, and turning lights. White for the ground wire, Brown for the running wire, Yellow for the wire going to the left stop and turn. Green for the wire going to the right stop and turn. In most cases, the blue wire, regardless of whether it’s on a utility trailer, RV trailer, or toy hauler trailer is normally for your electric brake circuit. It’s also important to know that Interior 12 volt lighting and secondary power needs do not have set, color code requirements.

Your tow vehicle may have amber left and right turn signals that operate independently of the stop and turn light. If this is the case, you need a taillight converter. All trailer systems, including RV trailer, cargo, heavy duty, and dump trailer models utilize a 2-wire system. Tow vehicles with separate turn and stoplights use a 3-wire system. A “tail light converter” converts the 3-wire feed to two.

The trailer running light, and stop and turn light system, is easy to work on as long as you take it, one circuit at a time. You don’t have to worry about reading complicated schematic diagrams to rewire your lights.

Whether you own an RV trailer, toy hauler or cargo trailer, the interior lighting operates separately from the trailer system.  Bear in mind, that unlike the wiring discussed here, the trailer’s interior wiring system is fairly complicated, much like the wiring in your home. Use these tips for the exterior wiring only. And, happy, well-lit, trailer trips to you and yours!

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