Parts Needed to Install 3rd Brake Light on Enclosed Trailer

Updated 07/09/2020 | Published 10/22/2018

Question:

Can this light be used as the third high marker light required for trailers over 80”? I think that it would be nice to have it function as a brake light as well. Just not sure if that’s DOT legal.

asked by: Rob

Expert Reply:

The Optronics light best suited to your application as a 3rd brake light is their part # STL80RB which is a single-function LED light. The light # STL64RB that you referenced is a multi-function light (Stop/Turn/Tail) which you do not need.

It is necessary that this additional light operate only with brake pedal signals and not with turn signals. You can meet this DOT requirement by installing a 2-to-3 converter which will separate the brake signals from the turn signals. Trailer wiring combines these functions but you need to provide a separate brake-only lighting signal for this center-mounted 3rd brake light to avoid the risk of confusing other motorists.

The converter takes in the combined stop/turn signals that are fed to your main taillights and outputs just a brake light signal on the red wire, which is what you will connect to the new light.

To help customers like you with questions about trailer lighting requirements our team put together a comprehensive article which I have linked for you. The article details the lighting and conspicuity treatments required based on trailer weight and dimensions.

expert reply by: Adam R

click to enlarge

Rob B.

7/5/2020

Hi there, Have a 2011 Acura MDX with a trailer hitch mounted bike rack that extends about 5 ft from the hitch itself. Would this light work as an additional brake light? And if so, would I need any additional parts? Thank

Chris R.

7/9/2020

You could certainly add the Optronics STL80RB to the rack to work as an additional brake light. You would just need to wire it into the Acura's brake light circuit so that it illuminates with the brakes.