Guide to Trailer Lights | The Trailer Parts Outlet

You can’t haul a trailer without proper lights in good working order. Let’s talk about common trailer light setups so you can know what to expect when you are getting your trailer lights up and running. Typical trailers have three circuits that hook up to your vehicle. One for the tail lights and one for each brake light, right and left.

The brake lights flash when you’re turning. This lets everyone know which way you’re going.

You need to have a ground wire for this system. This is a conducting path that’s separate  from the current circuit. Basically, it will keep the system from shorting out if there is an electrical surge.

If you’ve been following the arithmetic, that means you need four contacts for your wiring plug. Common trailer connectors use four pins plus a ground. These are usually flat plugs with a row of pins. It is relatively simple once you have your hands on the actual parts and vehicles. 

LED vs Incandescent Lights

Your trailer lights might come in two different varieties, LED or incandescent. LED trailer lights tend to last longer and be more durable. Incandescent trailer lights are often affordable and radiate a warmer color.

Other Light Setups

You might find connectors with five, six, or seven pins. They link together using round plugs like electrical sockets. The fifth, sixth, and seventh pins are for running other lights like those on the side or front of the trailer. Some might even power interior lights for work trailers, campers, or horses. 

Testing Your Four-Pin Trailer Light System

To test your four-pin trailer light system

  • Start the vehicle. Make sure the trailer tail lights illuminate
  • Tap the brakes to make sure those light up too
  • Use the turn signals and make sure those light up

If you can check all those boxes you are ready to go! All you need to do is add more checks depending on what other lights you are running on your trailer. 

Breaking Down Trailer Plugs and Sockets

Trailer plugs and harness plugs come in all shapes and sizes. A common design for a trailer plug and socket is a color-coded device with four wires. Often, the brown wire is for the tail lights, side markers, and license plates. The yellow wire runs the left hand turn signal and brake lights. The green wire powers the right hand turn signal and brake lights. The white wire is for grounding purposes. 

By the way, if you’re looking up parts and wiring systems for different trailers, you might come across the term, “poles.” That is a synonym for the number of wires.

Five Pole Systems

Remember, as discussed above, you might find a five-wire system. The first four are the same as the four-pole system. The fifth wire is blue. You use it for hydraulic disk brakes or auxiliary outlets. 

Six Pole Systems

For the six-wire systems, you already know the first five because they’re the same as those discussed above, but add a red wire that serves as a 12-volt feed. It runs devices like car alarms and cigarette lighters. 

Seven Pole Systems

And yes, this is as easy as you think. Seven-wire systems have the first six that you already learned plus an extra pole that powers things like the interiors of campers.

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