How to Wire Running Lights on a Trailer

Embarking on a trailer lighting project? Wiring running lights on your trailer is a crucial step to ensure safe and legal towing. This comprehensive guide will walk you through the process, from understanding your trailer's lighting needs to the step-by-step wiring process. Let's dive in!

Before we start, it's essential to understand that trailer lighting regulations vary by location. Always check your local laws and ensure your trailer is equipped with the required lights. Typically, trailers need tail lights, brake lights, turn signals, and license plate lights. Some may also require side marker lights and clearance lights.

Planning Your Trailer's Lighting System

First, assess your trailer's lighting needs based on its size and the regulations in your area. Then, choose the appropriate lights and wiring components. Here's a simple breakdown:

1. **Tail and Brake Lights**: These are mandatory for all trailers. They alert following drivers to your actions. Choose lights with the correct wattage and voltage for your vehicle's system.

Choosing the Right Lights

When selecting lights, consider their size, shape, and mounting style. Ensure they're compatible with your trailer's fender or bumper area. Also, check their IP rating for water and dust resistance, especially if your trailer is exposed to harsh weather conditions.

For example, LED lights are popular for their durability, energy efficiency, and bright output. They're available in various styles, including round, rectangular, and flush-mount designs.

Gathering Necessary Wiring Components

You'll need a wiring harness that connects your trailer's lights to your tow vehicle's electrical system. This usually includes a 4-pole flat trailer connector. Also, gather appropriate wire gauges, connectors, and tools like wire strippers, crimpers, and electrical tape.

For instance, use 12-gauge wire for tail and brake lights, 14-gauge for turn signals, and 16-gauge for license plate lights. Always follow the manufacturer's recommendations for your specific lights and harness.

Wiring Your Trailer's Running Lights

Now that you've planned your lighting system and gathered the necessary components, it's time to wire your trailer's running lights. This process involves connecting your lights to the wiring harness and then to your tow vehicle's electrical system.

Before you start, ensure your tow vehicle and trailer are on a level surface and the trailer's jack is securely chocked. Also, disconnect your trailer from your tow vehicle and turn off both vehicles to prevent any electrical shorts.

Wiring the Tail and Brake Lights

Start by connecting the tail and brake light wires to the appropriate pins on your trailer's wiring harness. Typically, the left wire goes to pin 1 (tail lights) and the right wire to pin 2 (brake lights). Use wire connectors or crimp on connectors, ensuring a tight, secure connection.

Next, run the wires along the trailer's frame, securing them with wire ties or cable clamps every few feet. Ensure the wires are protected from moving parts, sharp edges, and potential damage. Once the wires reach the tail lights, connect them to the appropriate terminals on the lights.

Wiring the Turn Signal Lights

Connect the turn signal light wires to the appropriate pins on the wiring harness. The left turn signal usually goes to pin 3, and the right turn signal to pin 4. Again, ensure a tight, secure connection.

Run the turn signal wires along the trailer's frame, securing them as you go. At the turn signal lights, connect the wires to the appropriate terminals. Ensure the lights are functioning correctly by testing them with your tow vehicle's turn signals.

Wiring the License Plate Light

The license plate light wire connects to pin 5 on the wiring harness. Run this wire along the trailer's frame, securing it as you go. At the license plate light, connect the wire to the appropriate terminal.

If your trailer has side marker or clearance lights, follow the same process for each light, ensuring they're connected to the correct pins on the wiring harness and the appropriate terminals on the lights.

Before reconnecting your trailer to your tow vehicle, test all your trailer's lights to ensure they're functioning correctly. Once you're satisfied with the lighting system, reconnect your trailer and enjoy safe, legal towing!