Troubleshooting Trailer Wiring And Brake Controller When Getting Error Codes

Question

Question:

I have a trailer equipped with electric brakes. All the lights and side markers were installed with grommets so there is no screws to ground them to the trailer. The four wire for the lights runs thru the interior of the trailer and at each light the appropriate wire is connected i.e. brown, yellow or green as well as the ground wire so each light is individually connected to the ground wire coming from the tow vehicle. There is no ground wire connected to the trailer. The brakes are connected to the appropriate hot wire and grounded to a wire that is spliced into the ground wire that goes to all the lights hence only one ground wire for everything. The auxiliary wire is ran back to a switch that is in turn connected to a light inside the trailer. this light only has one wire coming out of it. The light is bolted to the inside of the trailer and I assume that is how it gets its ground even though there is not any ground wire connected to the trailer as I mentioned earlier. I have checked to make sure that the problem is not the tow vehicle or the brake controller. What is happening is that everything works fine but when I step on the brake the controller starts blinking S.H. or short. The controller is a Prodigy P2. If I engage the controller with its own button I get a reading of O.L. or overload. I tried a lot of different things to try and get things working. When I disconnected the ground wire from the lights the brakes worked fine but no lights. The trailer was not connected to the tow vehicle at this time but when I connected the trailer to the tow vehicle the lights and brakes both worked fine but there is still no ground wire to the lights only the brakes. I took the trailer for a spin down a gravel road and I noticed the lights starting to flicker quite a bit. I would have to assume that the trailer is being grounded thru the hitch and the bumpy road is causing it to make the ground unstable. Then I connected the ground wire to the trailer but not to the lights again the brake controller flashed S.H. At this point Im kind of befuddled. I was wondering if the live wire that is going to the light and being grounded to the trailer would be the cause of the problem? Hopefully you have a solution my problem. If you need more info please let me know.

asked by: Eric H

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Expert Reply:

This is a tough problem. We need to start with the signal you are getting to the brake controller. You said you are getting a code for a short when you step on the brakes. Since you said the tow vehicle and brake controller check out, and the trailer is connected to the tow vehicle, the problem would indicate there is a short somewhere on the trailer. This can be an exposed or cut wire between the trailer connector and the brake assemblies. There are times when bad brake magnets can also cause this. I have attached links to a couple helpful articles that explain how to check the magnets and also how to troubleshoot a brake controller installation.

You said you get an overload code when you use the manual override. The most common reason you get an overload code on your controller if the trailer is not connected is a damaged trailer connector on the vehicle or corrosion. Check the connector out and see if there are any signs of corrosion or damage and clean or replace as needed.

If everything checks out on the vehicle side you can check all the wiring on the trailer with the help of an assistant. Use a 12 volt battery and use jumpers. attach the negative post of the battery to the ground pin on the connector. Then use another jumper and attach it to the positive battery. Attach the other end to each of the other pins on the connector. Have someone wiggle each wire from the back of the connector all the way to each light to see if they blink as y9ou described. Look for signs of damage or pinched wires.

You can also check the brakes with the battery and jumpers. Just connect the positive jumper to the pin for the brakes, (usually blue). You will hear the brakes activate when the circuit receives power.

If you have added lights to the trailer, it could also be causing problems by being overloaded, but should not affect the brake circuit and brake controller.

expert reply by: Jeffrey L

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Troubleshooting Trailer Wiring And Brake Controller When Getting Error Codes

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