Troubleshooting Trailer Brakes That Stay Locked Up

Question:

I have a 2009 Suzuki Equator Made by Nissan and I am having the same problem with the constant 12v going thru the blue wire. We did the switching of the blue and black wires but it seemed to not let me have brakes. My brake controller still flashed the S.H on it , which it is saying there is a short. we checked the magnets, all the wiring on the camper and still no brakes. we even checked to see if the controller was bad and that was shows it is good. so what else could I do?

asked by: Tony P

Expert Reply:

I suggest disconnecting the trailer to allow you to test the wiring on the vehicle independent of any potential issues on the trailer. You will need a circuit tester like # PTW2993 or a multi-meter like # PT89ZR.

First, test the 7-way. The brake circuit is carried on the pin at the 5-o-clock position (see photo please). If your controller is set for zero power and zero boost, in other words powered up but with no output level, you should detect close to 0 volts on the pin. If you detect 12V on this pin with the controller set to zero output then either the controller is bad or there is a short inside the 7-way or in the vehicle wiring.

7-way sockets and plugs can develop internal corrosion. This can be difficult or impossible to see from the outside. Over time moisture can migrate into the interior of these sockets and plugs and cause two adjacent circuits to become bridged together. Disconnect any wiring to the 7-way that you can and inspect it internally for any corrosive build-up or even just trapped foreign material like water, dirt or a stray strand of wire.

You can also test the trailer on its own using the car's battery or a spare 12V. When you apply this 12V battery power and ground directly to the contacts on the trailer's 7-way plug you should be able to hear and feel the trailer brakes engage. They should lock up or get close to locking up with this full power reaching the magnets. If the brakes do not respond in this way then there is something wrong on the trailer side. You can also apply the battery power directly to the brake wire leads right at the wheel by cutting them; this test will bypass the trailer wiring. If the brakes engage when directly powered then you know the issue is in the trailer wiring upstream of the brakes.

If you suspect your 7-way plug is corroded internally you can replace it easily and splice the other trailer wiring to it using a junction box kit like # HS381-9000. This includes a 7-way trailer plug, connectors, wire loom and junction box.