trailer brake question

[notjustair]

I have a 35 foot deck over that I usually pull with one of the semis hauling bales. I used it
about a month ago to haul a tractor the neighbor (with the Freightliner) and all was well. I went
to hook it to the Dually and the brakes won't work. I haven't hooked it to the 2018 Dually, but I
can't imagine anything is wrong with it since I unhooked the stock trailer to change it over and
it works fine on that. It worked on the 04 Dually that I traded in this summer, so I am sure it
can't be the difference in truck wiring.

It sits out. I am wondering about the breakaway setup. Do those control boxes go bad? When they
do is it a situation where the brakes don't work at all, or do they apply and never release. All
of the other wiring is fine, but the odd thing is that the brakes have red and black wires going
to them not blue, so it is kind of hard to chase (the trailer is an L&L). The breakaway box has
two blue wires going through it. The trailer is grounded through a white wire as usual.

Admittedly, I have always had new large trailers with brakes so never had a need to mess with
them. I don't even know how the magnets work. Are they hot and ground and then the voltage
decreases with use, or are they grounded and voltage is sent to them to apply?

I remember that when I started using the semi there was something that was backwards - that semis
have two of the wires reversed in comparison to pickups. I can't remember what wires it was, but
I had it worked on and since then it has always worked on either of the semis and the pickup.
Worse yet, my trailer dealer that got this one all set up when it was new has since died so I
can't pick his brain!

 

[Michael Soldan]

Hook the trailer up with all the plugs, then run a jumper cable from the truck to the trailer,make sure each end of the jumper cable is on clean bare metal, this will establish a ground and everything should work. I can tell you that 99% of all light failure on trailers id due to a bad ground between the two vehicles.

 

[jon f mn]

The break away is just an on/off switch hooked to a battery, they can stop working or short to on. I don't see how that could effect braking otherwise.

 

[Welding man]

I can't even remember the times that I have been called to work on trailer brakes that the family dog or a cow had chewed the wiring off the trailer. The magnets are a simple magnetic coil, they have no polarity. The more power you put to them the stronger they get. They do wear out and they do short out. The mechanical linkage that actuates the shoes also freeze up on the pivot arm pin and the brakes won't work. Nothing complicated about them, just a process of elimination.

 

[Steve@Advance]

It's really not that complicated, just need to have a test light and start tracing the brake wiring.

There is a lot of miss information out there on the terminal designation of the plug, that and front view/rear view, truck end/trailer end. Just be careful you are wired correctly and tracing the correct wire.

Typically the blue wire is the brake, terminal 2 on a 7 way plug.

To get power to the blue wire, either block the brake pedal down, or if the controller has a manual over ride, block it over in the applied position.

The magnets are wired parallel, each has it's own ground, usually grounded to the frame at each wheel.

If the trailer was wired with the fold over quick connector wire splices, that is the first place to look. They are worthless, should be replaced with soldered and shrink tubes connections, or at least crimp connectors.

The break away battery should not be able to keep the brakes from working.

A very common place for failure is in the trailer plug. The wires get loose and pull out of the screw connectors. Also on the truck side, there is a battery connection that is always powered up. That is a common place for corrosion to grow, especially if it gets wet.
7 Way Connector

 

[VADAVE]

Are you sure the brakes don't work?
Since they're electric it could be as simple as a skim coat of rust on the magnets or the drum. Electric brakes work by a magnet pulling to the drum and then the drum rotating a lever the end of which resides between the shoes and is square. As the square end of the lever is rotated the shoes are pushed out to contact the drum thus applying the brakes. Setting out with rain and snow the magnets and the drums will rust a small amount and the shoes will slip until the rubbing of the magnets against the drum and the shoes against the drum rub the rust off. I usually go down the lane with the brakes full on--by the time I get the road the rust is gone and the trailer wants to stop. If not it's time to get out the meter and chase the voltage.

 

[jeffcat]

Hey, thanks for that nice wire diagram!! My Ford Expedition is set up with the trailer package. It has both types, 4 and 7 pin plugs. Only thing that ever screwed it up is when the ground connection got a tiny bit of corrosion to the frame. Fixed it but only took about five minutes to find it. You really want that ground. Through the trailer hitch ball ain't going to cut it!

 

[showcrop]

I have a test light with 4-5 indicators that plugs into the truck that verifies that the output of the truck is what you think it is.

 

[Determined]

(quoted from post at 12:44:50 02/08/18) I have a 35 foot deck over that I usually pull with one of the semis hauling bales. I used it
about a month ago to haul a tractor the neighbor (with the Freightliner) and all was well. I went
to hook it to the Dually and the brakes won't work. I haven't hooked it to the 2018 Dually, but I
can't imagine anything is wrong with it since I unhooked the stock trailer to change it over and
it works fine on that. It worked on the 04 Dually that I traded in this summer, so I am sure it
can't be the difference in truck wiring.

It sits out. I am wondering about the breakaway setup. Do those control boxes go bad? When they
do is it a situation where the brakes don't work at all, or do they apply and never release. All
of the other wiring is fine, but the odd thing is that the brakes have red and black wires going
to them not blue, so it is kind of hard to chase (the trailer is an L&L). The breakaway box has
two blue wires going through it. The trailer is grounded through a white wire as usual.

Admittedly, I have always had new large trailers with brakes so never had a need to mess with
them. I don't even know how the magnets work. Are they hot and ground and then the voltage
decreases with use, or are they grounded and voltage is sent to them to apply?

I remember that when I started using the semi there was something that was backwards - that semis
have two of the wires reversed in comparison to pickups. I can't remember what wires it was, but
I had it worked on and since then it has always worked on either of the semis and the pickup.
Worse yet, my trailer dealer that got this one all set up when it was new has since died so I
can't pick his brain!

I have been dragging my 30 foot stock trailer around with a 98 GM dually for 12+years, put all new brakes and wiring on it when I first got it.

Typical cattle farmer as long as it was working so so it was good enough for what I was using it for, I knew the brakes were not as good as they were when I first got it, they still worked as did all the lights so the wiring I figured was fine.
The controller lit up when the truck was hooked to a trailer and the lights and numbers on it responded to truck braking.

Must be the shoes need to be adjusted, ya I will get to it someday.

A month ago I replaced my worn out GMC with a 2006 Chevy 1 ton dually.
The first time I hauled the trailer with the new truck the brakes were locking up and I had to turn down the controller.

Long story short regardless of what a controller says it is doing don't trust it.

 

[Hobo,NC]

They make a plug in tester for those 7 ways its worth it weight in gold. I think they are around $20 its money well spent to eliminate the truck side...

 

[Bkpigs]

Turn on p the controller and have someone push the brake pedal. If you don't hear humming then you have an electrical issue. If you hear humming from the magnets then you have a mechanical issue in the brake assembly.