Troubleshooting Trailer Brake Lights not Working When Running Lights are On
Question:
I put all new trailer lights and wireing on my Boat trailer. Lights work, turns work. I am pluging into an adapter 7 pole to 4 pole and 5 pole. When I have the lights on and put on the brake the lights go out. When I turn off the lights and put the brake on the Lights work. What am i doing wrong? The only thing I did not do that I saw in your videos is I did not sand off the paint, and rust. Could that be it? Thanks for your time and Videos Please help
asked by: Dave M
Expert Reply:
It sounds like you might have a bad ground connection. When the taillights are on, that is when there is the most power draw on the system. Stepping on the brakes would then add more and this is when a ground problem will usually show up.
The taillights usually ground through the mounting bolts on trailers. Check for a bad ground, loose connection, and dirt and corrosion. Any of those can cause this problem. Also check the light bracket connections to the trailer frame as lights can ground through the mounting studs.
If you used a plastic license plate frame or bracket behind the left taillight instead of a metal one, that could be causing the problem as well.
I have included a video on the procedure for checking for a proper ground.
There is also an FAQ article on trailer wiring. Near the end of the page, after the plug diagram section, there is a section on weak grounds. I have included a link to this article below.
![Michael H](https://images.etrailer.com/static/images/catg/people/324_tn.jpg)
Product Page this Question was Asked From
Adapter 7-Pole to 4-Pole and 5-Pole
- Trailer Wiring
- Wiring Adapters
- Multi-Function Adapter
- 7 Round - Blade
- Plug Only
- 4 Flat
- 5 Flat
- Hopkins
more information >
Featured Help Information
Miscellaneous Media
Continue Researching
- Q&A: Trailer Brake Lights Do Not Work when Running Lights are On
- Article: Trailer Wiring Diagrams
- Shop: Trailer Wiring
- Shop: Hopkins Plug-In Simple Vehicle Wiring Harness with 4-Pole Flat Trailer Connector
- Q&A: Troubleshooting Trailer Taillights that Dont Blink When Running Lights are On
- Article: Brake Controller 7- and 4-Way Installation Kit (ETBC7)
- Search Results: hitch
- Q&A: What is the Difference Between a Class II and a Class III Hitch?
- Video: Choosing the Right Trailer Wiring
- Shop: Trailer Hitch
- Shop: Curt Powered Tail Light Converter with 4-Pole Flat Trailer Connector
- Shop: 7- and 4-Pole Trailer Connector Socket w/ Mounting Bracket - Vehicle End
- Q&A: Lug Nut Torque Chart for Trailer Wheels
- Shop: Brake Controller
- Article: Trailer Tire Sizing
- Search Results: trailer hitch
- Video: Tow Ready 4-Pole Mounting Bracket Installation
- Shop: Universal Installation Kit for Trailer Brake Controller - 7-Way RV and 4-Way Flat - 10 Gauge Wires
- Q&A: What is the Difference Between a 4-Way and 7-Way Trailer Connector
- Search Results: trailer brake controller
- Article: How to Measure Your Trailer Wheel Bolt Pattern
- Shop: Gooseneck Hitch
- Search Results: brake controller
- Shop: Tekonsha Prodigy P3 Trailer Brake Controller - 1 to 4 Axles - Proportional
- Q&A: What is the Difference Between Load Range C and D ST175/80D13 Trailer Tires
- Search Results: fender
- Shop: Fifth Wheel Hitch
- Shop: Curt T-Connector Vehicle Wiring Harness with 4-Pole Flat Trailer Connector
- Q&A: Which is Better for Highway Use 4.80-12 or 5.30-12 Trailer TIres
- Article: Wiring Trailer Lights with a 7-Way Plug (It's Easier Than You Think)