Chosen Solution
installed new trailer lights, and if I have the running lights on the car on, and press on the brakes all the lights go off on the trailer until I let off the brake
Hi, Check that there is a good earth (ground) connection between the vehicle and the trailer.
I would also make sure the lights have a good ground connection to trailer frame and the pigtail (4 or 6 pin) also has a good ground connection to trailer frame.
