Trailer Brakes Locked Up

MotorCityBear · Oct 30, 2019

First post and I need some advice.

I just bought a used trailer off of craigslist. The trailer (16x6.5) is in great shape and has electric brakes.

When I bought it, as soon as I plugged (round 7 pin connector)it into my 2019 Chevy Colorado, (with the trailer tow package and integrated trailer brake controller) I got a service trailer brake system message on my dash and the trailer brakes were locked up.

I unplugged the trailer, plugged it into the Seller’s F-150 and everything was OK.

So I took my truck into the Chevy dealer thinking the trailer brake controller module was bad but they said there is no problem with my truck.

The Seller then brought the trailer to my house with no issue.

So my question is, where do I start trying to diagnose this problem.

I thought trailer wiring was basically the same on all vehicles, trailers, but could the trailer be wired differently?

Any advice would be much appreciated.

Thanks for reading this far!

4570Man · Oct 30, 2019

I guess the possibility exists that the seller has wired his truck wrong and then wired the plug wrong to match his truck but I’m guessing it’s an issue with your truck wiring.

WM75Guy · Oct 31, 2019

If he wired in an aftermarket brake controller he may not have used the standard wiring configuration. He may have swapped wires on the trailer to make it work. I would start by opening up the trailer plug. Here is the standard wiring schematic.

I bought one of these wiring checkers for less than $20 at O'Reillys. Well worth it to let me know if the truck is the problem or the trailer. Much easier than a test light, which is also handy to have.

Roadworthy · Oct 31, 2019

Start with how many pins are on the trailer connector. I think seven is standard now but with the six pin connector there were two different "standard" configurations. If your truck has the current standard seven pin connector and the trailer does as well the trailer needs wired to match the truck. Look especially at the brake controller pin and the auxiliary power pin. Sometimes these are swapped and if they are you are locking the brakes whenever you connect the trailer.

4570Man · Oct 31, 2019

Did you verify the brakes actually worked behind the F-150 and weren’t just disconnected? In any case I think it’s a relatively simple wiring issue.

mrmikey · Oct 31, 2019

I just put electric brakes on my trailer that I tow with a 2015 Frontier. It's prewired from the factory, all I had to do was mount the controller and plug in the harnesses to the truck wiring. Looking thru the instructions, there was a warning that some year Frontiers had the constant 12V and the trailer brake output inserted into the wrong side of the plug on the rear of the truck from the factory. Sure enough, mine was one of them so I had to reverse the two wires, not a big deal but it would have been a head scratcher for a bit 'tll I figured it out. Symptoms would have been the same as yours..........Mike

Redlands Okie · Oct 31, 2019

A few years ago we had quite a few issues with swapping trailors between ford and dodge. On my dodge the running / parking lights would lock the trailor brakes. The two wires were opposite. I have a factory made adapter plug that I use when I run into this problem. Save me from having to rewire some one else’s trailor to temporarily use on my dodge. A rental yard I use a lot has ford trucks. The last couple years the problem seems to have mostly gone away. I assume that most use the same wiring pattern now.

skipperbrown · Oct 31, 2019

You need to get a voltmeter and a helper and check each pin to see when it has voltage and confirm your ground pin. My guess is that you have incorrect wiring on the trailer but you will need to know when/where voltage is coming out of your truck and where it is going on the trailer.

ovrszd · Oct 31, 2019

Redlands Okie said:
A few years ago we had quite a few issues with swapping trailors between ford and dodge. On my dodge the running / parking lights would lock the trailor brakes. The two wires were opposite. I have a factory made adapter plug that I use when I run into this problem. Save me from having to rewire some one else’s trailor to temporarily use on my dodge. A rental yard I use a lot has ford trucks. The last couple years the problem seems to have mostly gone away. I assume that most use the same wiring pattern now.

Yep. I've saw this before. Some Fords didn't follow the standard wiring schematic. The suggestions and diagrams above will resolve the problem.

mrmikey · Oct 31, 2019

There was a thread here I think it was years ago. It was a four way stop intersection that a 1500 series truck pulling a trailer went thru and hit a car. The truck driver said he tried to stop but the weight of the trailer pushed him thru. The skid marks for the trailer were dashed, similar to a broken crossing line on a highway only black rubber skid marks, whoever had wired the trailer up had wired the lights to the turn signal circuit and the brakes would pulse with the turn signals. The driver said he had never needed to panic stop since he had the trailer and never noticed it before..............Mike

MotorCityBear · Oct 31, 2019

I will check the wiring on the truck and trailer for a mis-match and hopefully I just need to change a few wires in the trailer. I know the trailer brakes work, as they locked up as soon as I plugged it into my truck and released as soon as I unplugged them.
Thanks for the help!
Rob

aczlan · Oct 31, 2019

MotorCityBear said:
I will check the wiring on the truck and trailer for a mis-match and hopefully I just need to change a few wires in the trailer. I know the trailer brakes work, as they locked up as soon as I plugged it into my truck and released as soon as I unplugged them.
Thanks for the help!
Rob

if there is a mismatch, I would use the wiring diagrams found above to make it so that both sides match the standard. That way another vehicle can tow your trailer or you can tow another trailer with your truck.

Aaron Z

4570Man · Oct 31, 2019

mrmikey said:
There was a thread here I think it was years ago. It was a four way stop intersection that a 1500 series truck pulling a trailer went thru and hit a car. The truck driver said he tried to stop but the weight of the trailer pushed him thru. The skid marks for the trailer were dashed, similar to a broken crossing line on a highway only black rubber skid marks, whoever had wired the trailer up had wired the lights to the turn signal circuit and the brakes would pulse with the turn signals. The driver said he had never needed to panic stop since he had the trailer and never noticed it before..............Mike

I gotta call bs on that one. First problem is with no controller and straight 12 volts the brakes will be locked. He never noticed the trailer brakes being applied every time the turn signals blinked? Yea right. Next problem is the trailer brakes are way higher amperage than the turn signals and would have probably blown the fuse after the first application leaving you with no trailer brakes at all.

MotorCityBear · Oct 31, 2019

So I checked the truck and it is wired identical to the picture REPowell posted(thanks for the pic). So I guess that is right.

I need to start checking the trailer now but holy crap, it is like 41 degrees and windy. I am in GA, what the heck is going on with the weather!

aczlan · Oct 31, 2019

4570Man said:
I gotta call bs on that one. First problem is with no controller and straight 12 volts the brakes will be locked. He never noticed the trailer brakes being applied every time the turn signals blinked? Yea right. Next problem is the trailer brakes are way higher amperage than the turn signals and would have probably blown the fuse after the first application leaving you with no trailer brakes at all.

I have to disagree. We towed a 7,000# trailer behind our Dodge 1500 that was wired with the turn signals to the brake wire.
No fuses blown, just brakes every time we turned on the turn signal.

Aaron Z

Mancelona Man · Oct 31, 2019

Not sure on Chevy.... but my Nissan Frontier had the brake wire and constant 12 volt for break away battery reversed. I had to cut and splice in the wire harness under the truck and crisscross them.

4570Man · Oct 31, 2019

aczlan said:
I have to disagree. We towed a 7,000# trailer behind our Dodge 1500 that was wired with the turn signals to the brake wire.
No fuses blown, just brakes every time we turned on the turn signal.

Aaron Z

But you noticed right away right?

mrmikey · Nov 1, 2019

gotta call bs on that one.

Just what I read and saw in the pics of the skid marks.

aczlan · Nov 1, 2019

4570Man said:
But you noticed right away right?

We picked it up from a friend's house, didn't notice till we got half way home. Probably wouldn't have noticed it as much if it had been empty.

Aaron Z

Dftodd · Nov 1, 2019

What's kind of common as well is someone not familiar with the color codes between a 4 pin and 7 pin plug. They tend to apply a 4 wire color code to the 7 pin which will make your trailer lights go wonky as well.

Yellow is aux power (battery charge) on a 7 pin, red is left turn, brown is right turn, and green is parking lights.

You get someone used to wiring 4 wire plugs and it gets interesting. Especially when they are using a trailer light that comes wired for a 4 pin connector.

They plug it in and the left light stays on all the time, right turn will cause both lights to blink. Left turn won't do anything, and parking lights will turn on the right light. :laughing: