FAQs: Trailer Lighting

Trailer Lighting System

We get asked questions about trailer lighting quite frequently here at Gooseneck Trailers. Here are some of the most frequently asked questions.

What is the Difference Between Lights That Have a “C” in the code (PC and PC2) and those that don’t (P2 and P3)?

P2 or P3 emits a light beam that spreads out 45 degrees to each side of its centerline for a total of 90 degrees of coverage. While this beam pattern can be seen straight on, it cannot be seen clearly from the side of the trailer. When these are mounted to the front, sides or back of a trailer, this kind of light provides adequate visibility.

The PC emits a light beam that spreads out 90 degrees to either side of the centerline for a total of 180 degrees of coverage. Not only can this beam pattern be clearly seen when you are standing directly in front of the light, but you can see it when you are standing on either side of the light as well. This wide angle beam allows the light to perform not only as a front clearance light, but also as a side marker light.

Performing its combined functions requires a PC light to be properly mounted. Some lights are designed to mounted at a 45-degree angle between the front and side or between the side and back of the trailer. These lights must be mounted on a part of the trailer that provides this 45-degree angle. There’s other PC lights that emit light through 2 lenses in which 1 lens faces towards the front or back of the trailer while the other faces toward the side. To be visible from the side of the trailer, these lights must be mounted square to the back or front of the trailer and at the outer edge.

What Does it Mean When a Trailer Light is for Trailers Wider than 80″?

Front and rear clearance lights and rear identifications lights are required on trailers that are 80″ (6’8″) or wider at the widest point point, in addition to basic trailer lights. These clearance lights are used to indicate the width of the back the trailer. Only one rear clearance light is required at each side on the back of the trailer at the trailer’s widest point. These clearance lights should both be at the same height and as high as possible unless identification lights are mounted on top. In this case, the clearance lights can be mounted lower. A light that functions as a rear clearance light can be designated as a light for 80″ wide trailers, whether the light is combined with other functions or it is intended only as a clearance light.

Rear Clearance Lights Combined with Other Lights

The back of the trailer is most likely at its widest point if the bed of the trailer extends out past the wheels. If this is the case, you can use combination lights that are designed specifically for trailers wider than 80″ and that have the clearance lights built in. These lights should be mounted at the widest point of the trailer at the rear.

Combination lights are most commonly used on flat bed utility trailers. Rear clearance lights are required to mounted low on these trailers because there is no place above the frame on which to mount the lights.

Rear Clearance Lights Separate from Other Lights

The fenders most likely create the trailer’s widest point if the trailer’s wheels extend out at the sides beyond the bed of the trailer. If this is the case, you can use standard combination stop lights, tail lights and turn signal lights just for those functions and mount separate lights on the fenders to mark the rear clearance.

A combination light made for trailers greater than 80″ should not be used for this application, even though the trailer is wider than 80″. Although, the rear clearance lights could be designated for trailers that are 80″ wide.

Combination lights that include rear clearance lights would also not be used on a tall trailer either. The rear clearance lights on a tall trailer should be mounted high on its body and away from the tail lights.

What’s the Difference Between Non-Submersible, Submersible and Waterproof Lights?

Non-Submersible Lights

Non-submersible lights are not designed to be submerged. While the lens may may have a seal or gasket to help keep water out, that may not be enough to guarantee that water won’t get into the light assembly.

Submersible Lights

Submersible lights are designed to avoid damage if they are submerged. Manufacturers use 1 of 2 methods to improve the ability of a light to resist water damage.

  1. Adding a drain hole at the bottom of the light. This design is meant to let out water out if it does get in. A short submersion won’t necessarily damage the light. Also, because the hole is located at the bottom of the light housing, the air that is trapped inside the light will help keep water away from electrical connections.
  2. Sealing the light so that water can’t get in is called a waterproof light.


These are just a few of the frequently asked questions about trailer lights. For more information, don’t hesitate to contact us here at Gooseneck Trailers!

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