Trailer Brakes Lock Up with Miswired Brake Controller and Trailer Connector


I have an activator by draw tite P/N 5100 , SN 536462. It came with the truck I just bought. A 2001 dodge Ram 3500 4 x 4 dually. It was not hooked up correctly both black and white were on the positive post of drivers side battery and 7 pin draw-tite plug was corroded and right and left turn signal were swapped. I put a new 7 pin draw-tite plug and wired to standard configuration what all my other trucks have And what the instructions suggest. All wires are separate not from harness. Red wire IS on the cold side of brake switch. I have two 5200 # Dexter axles with four brakes total. It worked fine for two days short trips in town, running settings near or at max 10,000# load. Then one night I pulled up to a traffic light and when I went to pull away the trailer brakes remained on. I pulled into a parking lot and fiddled with the set-up. If I would remove the fuse in the 12volt supply line to controller the brakes would go off and stay off. I would replace the fuse and brakes would be fine starko OFF but when I either applied the manual OR foot brake the brakes will come on and stay on??? Oh!! by the way the indicator light located near the output control never came on at all?? But the output control switch functioned fine. PS I would have installed a new Tekonsha Prodigy P2 controller that we bought from you guys, albeit several months ago. We bought it just to have in stock and maybe to get free shipping on the order,,LOL but when we opened the box there was no wiring harness the little 4-wire plug that goes into the back of unit.. do they normally come with unit or is it a separate purchase. If part of unit, how can we get one?? PPS How can I wire trailers so that the trailer battery will charge while driving they dont have to periodically use a battery charger. Trailers are electric over hydraulic dump trailers?


Expert Reply:

Given that the brake controller was wired for both power and ground to the positive battery terminal that pretty much destroys the controller. You are going to need to replace it. Since everything else was working at one time it sounds like you have corrected the wiring issue. To be sure I have included a link to our wiring FAQ article that has diagrams that show how various connectors are wired.

Something seems to be applying full power to the trailer brakes whether it be a short or something that is miswired. By following the diagrams you can make sure your connector is wired properly. A short could have come from the improperly wired controller or even from a dirty or corroded vehicle or trailer side connector.

I do recommend using the P2 # 90885. It is supposed to come with a plug with 4 blunt cut wires, # 7894. If your package was missing this part please call customer service at 800-298-8924. White is ground and goes to the negative battery terminal. Black is 12 volt power and goes to the positive battery terminal via a 30 amp circuit breaker, # PK54530. The red wire goes to the cold side of the brake switch. And blue is output to the trailer connector. Or if the truck has the blue connector on top of the white junction box on the firewall behind the emergency brake pedal you can use connector # 3020-P.

The most likely scenario is there is a short or corrosion that is jumping to the brake circuit. Once you have everything re-wired on the truck with the new controller if it still does the same thing chances are that it is a problem on the trailer side. I have included a link to an FAQ article on testing brake magnets that should help.

As far as wiring up a trailer and vehicle to charge a trailer battery, the short answer is you cannot. You can only provide a maintenance charge that will maintain the current charge level of the battery but will not up-charge it. You would just connect a wire from the 12 volt circuit on the trailer connector to the positive battery terminal.

To charge the batteries correctly I do recommend the use of a battery charger like CTEK # CTEK56158. I own this battery charger and it works quite well.

expert reply by:
Michael H

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