Trailer wiring

[Turbo4whl]

Some info that may help with all wiring upfits. I had a trailer with electric brakes for a safety inspection. Trailer brakes would work with the brakeaway cable pulled, but not through the truck/trailer plug. I found the builder used sealacrimp conectors.

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Notice the connector upper left with blue wire. The seal over part of the loop prevented the nut from tightening the nut to the metal loop. You can also see how a new connector, upper right also has sealing plastic on the loop, just not as much.

This trailer, two axle 12x4" brakes has a GVRW of 19,300 pounds. It can carry 3 large cable reels. Here is the factory wired connection box. (I use the word factory loosely)

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[bucket]

Hey I've got a somewhat related question that you may know the answer to. We got 4 new International medium duty trucks and we ordered the "in-dash" trailer brake controllers. Well, it turns out, that option simply means that the dealer installs an aftermarket brake controller to the underside of the dash. It's a joke really. But anyway, all 4 trucks will apply braking power to a trailer, but they do not show connection on the controller so it makes it a real guessing game to adjust brake bias. I haven't had much time to investigate... do you have an idea of what they might have done wrong? It's only 4 wires, I don't know what they could have possibly done.

 

[Turbo4whl]

@bucket

What brand is the aftermarket controller?

 

[bucket]

@bucket

What brand is the aftermarket controller?

It's this model:

https://www.etrailer.com/Trailer-Brake-Controller/Tekonsha/TK29ER.html?feed=npn

Not a fancy one with a display, just the led indicator that's supposed to light up green when connected, then turn to various shades of orange and red as the brakes are applied.

 

[bucket]

Also, something else that puzzles me is the wiring at the back of the truck. We ordered the optional rear body harness as well as a trailer plug harness. As delivered, the wires are not labeled for function, some of them are odd colors and many of them are just orange. The dealer we purchased the trucks through could not provide us with a schematic of any kind. I went through and figured them out, but each truck has a wire that is a constant 5 volts. It's part of the body harness which are all heavy gauge wires (trailer harness plugs are all smaller gauge wires). Pretty dumb, I think.

Long story short, I have no idea what use there would be for a constant 5v supply. Even the 12v Aux power wires are ignition switched.

I forgot I have a picture of the body harness:

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[75gmck25]

A guess at two possibilities/guesses, considering that maybe these vehicles were wired for to serve an “international” market. However, very odd that the dealer would not have a wiring diagram.

- wiring of plugs for European trailer power/lighting is different, so I assume color coding of wiring is different. For example, on older Land Rovers you need to use an adapter to plug in to a standard US trailer.

- 5 volts is used for many modern electronic devices and adapters. Could it be 5 volt power for some other type of controller or adapter that is needed for certain conversion bodies?

 

[bucket]

I'm sure someone at the dealership could provide a diagram, but nobody we talked to could find one that was accurate.

The trailer harness is actually two separate weather pack connectors. The guys at the dealership couldn't find us any kind of pigtails to plug directly into them either. They are odd too, as one connector has two wires for LT and two wires for RT.

 

[Tonimus]

The +5V should be the actual brake control circuit. The red brake wire should be for the lights. The +5V should be pulsed and looking for a load when nothing is connected.

 

[bucket]

The +5V should be the actual brake control circuit. The red brake wire should be for the lights. The +5V should be pulsed and looking for a load when nothing is connected.

The one I have labeled as "brake 12+" is for the trailer brakes. It only gets voltage when the controller sends voltage. The brake lights are shared with the turn signal function (single lights). The 5v wire is just a constant. It's always 5v, no matter what the conditions are. The 5v wire is part of the "body" harness only. The brake 12v supply is in the "body" harness as well as the "trailer" harness.

 

[bucket]

Oh yeah, and with the "brake 12+" wired to the trailer brakes, it does operate the trailer brakes properly. The indicator just does not light up on the controller and setting the gain is a guessing game because of it. The controller also can't be properly leveled because the indicator is needed to do so.

 

[Tonimus]

Maybe this is the answer?

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[bucket]

Brake controllers are very simple to wire. They require a 12V+, a ground, a signal from the switched side of the brake light switch, and then an output wire to actuate the trailer brakes.

 

[bucket]

Maybe this is the answer?

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There's no standard color for the wires really. Function is the most important part.

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I've wired many many trailers and plugs. There's never been a 5v wire before.

 

[bucket]

One other thing, the "7-way heavy duty" plug with the red brake wire is used on stuff like road tractors and farm tractors that don't use a trailer brake controller. Road tractors have separate brake lights that function independently from the turn signals.

 

[Frankenchevy]

5v is almost always sensor or diagnostic related. I wonder if it’s for abs or stability. I’ve seen some trailers with ABS related features, but no idea how they work.