Trailer Lights Shut Off when Brakes are Pressed on a 1970 Sears Boat Trailer

Question:

I have a 1970 sears boat trailer, I just got done sanding and painting the trailer and put new lights on it the brand is Attwood submersible I bought them from wal-mart. The issue that I am having is that when I turn on my ignition my lights come on like they should on the trail blazer and the trailer but when I press down on the brake the lights shut off on the trailer other than that my signals work and flashers work. The other thing is when I shut the lights off on the car my brake lights and my turn signal lights work just fine I just do not have marker lights on the trailer. I sanded the paint back off where the light brackets bolt to the trailer and on the brackets but still no results. I have also tried plugging the lights in on a ford ranger and I get the same results. Please Help...Thank You.

asked by: Terry

Expert Reply:

It sounds to me like you have a ground issue somewhere on your trailer causing all of the lights to shut off since you have the same issue with multiple vehicles. The brake lights apply additional load on the circuits which is usually when a ground problem will show up.

First, make sure that the trailer connectors on the vehicle and trailer are clean and free of any corrosion. Corrosion can cause a short which can lead to many problems.

Next, check that the ground wires from the trailer connectors are connected to a clean, bare metal surface. Once you have verified that the trailer connector is in good condition and it is grounded properly, I would recommend checking that each marker light and tail light is grounded to a clean bare metal surface. Trailer lights will ground through either the mounting studs or they will have a ground wire coming from them.

I would also recommend following the trailer wiring from the connector back to the lights looking for any pinched, frayed or damaged sections of wire that could cause a short.

The marker lights on your trailer should be connected to the tail or running light circuit on your trailer. That circuit should only receive power when the vehicle tail lights are on. If you turn off the lights on your vehicle, then the marker lights are supposed to turn off as well, assuming the trailer is wiring correctly.

I have attached a help article on trailer wiring and a video that should help you out while you are troubleshooting this issue. If these steps do not resolve your problems, then let me know what you come up with and we can take further troubleshooting steps.

expert reply by: John H