Aiieee, this was so close to being a right answer, that it hurt. They were on the right track up until they said to take out a light bulb to fix the problem. No, no no!
Here’s the deal. The trailer has to have a ground wire in the harness and a brake wire. It might also have a brake light wire and a + voltage wire.
If it doesn’t have a separate wire for the brake lights, you’re pretty much screwed. There’s no way to get the blinkers to work.
If it does have a separate wire for the brake lights, then either (a) the wire for the light and the wire for the brake are reversed, or (b) the installer didn’t bother to run the brake wire up to the pedal and simply connected both wires to the brake light.
How to tell the difference? Easy. Turn on the car, turn on the blinkers, and get out and look at the trailer lights. If they’re not blinking, you’re in luck, and swapping the two wires should fix the problem. Testing with a meter will quickly show which is the right wire for the lights.
If the lights are blinking and the brakes are going on and off, then they’re both hooked to the lights. If the connector for the trailer harness has two separate pins connected to the brake lights, then run a second wire from the brake pedal down to the connector, split the two pins connected to the brake light, and hook one pin to the light and the other to the pedal. Trial and error will show which is which. If only one pin is connected to the lights, you’re screwed and can’t use the flashers.
Trailer brakes are really simple and ingenious. The varying voltage energizes an electromagnet with a friction pad mounted on a lever. The pad sweeps the rotating inside vertical surface of the drum. The magnetic attraction to the drum pulls the pad and the lever (which is not unlike a parking brake lever) to push the shoes against the drum in the normal fashion.
As I have thought about this situation, I am leaning toward a grounding problem of the trailer to the pickup. One thing I had not paid attention to was the beginning of the segment where the owner said that the brakes would not work then would grab, This would indicate that the current path for the electric brakes was not consistent i.e. the ground through the hitch was resistive.
I think the current from the running lights and flashers is returning to the truck ground through the servo coils of the electric brakes. The difficult thing to conceive is how the hot lead going to the brake actuator is finding gound in the actuator in the truck.
It has to be the way the control box is designed. When the truck brakes are applied, electrical power has to be applied to the electrical controller. It could be a reostat or a potentiometer. I have seen units that have a control handle that can be positioned to apply the trailer brakes appropirately. There are also controlers that are hydraulically actuated that move the electrical control in proportion to the brake pedal force applied.
One of these days I am going to get the opportunity to take one of those controllers apart.
I initially thought of grounding issue, until I thought about the controller. I’m assuming (and I
know nothing…) the controller HAS to be told the car in IN REVERSE (by the back-up light?)
or ANY REVERSE TRAVEL will be interpreted as HARD BRAKING, and would apply the trailer
brakes?