Trailer brake controller wiring

[zrain25]

Ok so long story short I am towing a 16 ft tandem axle now. Last week I fixed my messed up 7 way connector. Now I am trying to install a trailer brake control box. The guy before me took he's out before he sold it to me. So I have 4 bare wire under the dash and they are black,white,red,and blue under the dash. The brake box has the same colors so i butt connected wires together follow the control box instructions. I think it was the truck red wire was the hot and went to the boxes black wire. Blue to blue. White to ground. And now I'm left with the control box red wire with nothing to splice to. The instructions say to splice it to the light green brake light wire. I don't see any light green brake light wire. All I see is a black wire that looks like it use to connected. ???? I'm lost


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[jesilvas]

Which controller do you have?
Basically it's like this.
Blue is for the power OUT to the trailer brakes to energize them.
White is ground.
One wire will be the brake switch wire which, when the brakes are hit, it tells the controller to start feeding power to the brakes.
And a 12V wire that is probably switched but may be 24/7 hot. That is the source for the brakes.
Basically, a controller is a relay with a built in automatic potentiometer.

[zrain25]

Ya I have every wire except the brake light wire it is sapose to be a green wire and I don't see on at all


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[jesilvas]

Well you can just find one that turns hot when the brake lights come on or when the brake is applied.

[zrain25]

Ok it says to tap into the green wire. Wasn't there so I went to the brake pedal and unwrapped the brake pedal wires and found a light green wire. Do u think that wire would work?


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[jesilvas]

Idk test it.
That 'green' is probably part of the factory wiring.
You just have to find out what wire goes hot with the brake pedal stepped on.

[zrain25]

Ok thanks. One more thing is the brake box sappose to be on at all times or only when u plug the trailer in


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[jesilvas]

It's always there, and "on" is ambiguous. It's always receiving power from the 12V source, the brake switch wire, and always to ground. But, depending on the model, it will only say there's a trailer there when the circuit to the brakes becomes closed.

[zrain25]

Thanks alot


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[ttyR2]

My Tekonsha P3 is always on. The first time you hit the brakes after starting the engine, it will show a big circle/slash saying no trailer is connected if there isn't one hooked up. If there is, it'll show 0.0 when the brake isn't on indicating a trailer is connected but no braking force is being applied yet.

It'll even indicate if you have the wiring wrong. Evidently there are two ways to wire up a 7-pin plug and the adapter a friend loaned me was for the wrong way so the controller indicated a "short to battery" condition. Otherwise I wouldn't have known there was a problem.

The P3 is worth the money.

I'm assuming you don't have the factory trailer wiring option?