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The Trailer Breakaway Kit

What in the world is a Trailer Breakaway Kit?  If you pull a “larger-ish” trailer, you should definitely know, because it’s a legal requirement in many jurisdictions. It’s actually a pretty nifty concept.  However, there are some nuances, and for some in DIY, they are a little intimidating.

The concept of the “Breakaway” is to automatically apply brakes if a trailer comes disconnected from the tow vehicle.  We’ve seen how terrible this is — and even more terrible — it’s not that uncommon for a trailer to unhook.  People forget to tighten the hitch, or don’t get it on totally.  Either way, that’s where the trailer Breakaway Kit comes in.  It applies the trailer brakes if a disconnect does happen.  The idea, I guess, is that (hopefully) stopping a trailer is less of a hazard.  While there are arguments both ways, it’s the law for now, and until we have something better, this is what we do.

In most cases, this applies to trailers of more than 3000 lbs. GTWR (Gross Trailer Weight Rating).  This includes a lot of trailers built from plans we offer.

Please Note:  This article discusses the electrical breakaway, not other systems.

Electrical Actuation

While there are Hydraulic systems that can do this also, this article is for electric brakes.  It works with all Electric brakes and with the Electric over Hydraulic systems.

The concept is simple.  The trailer gets a battery so it has power to apply the brakes if needed.  There is a pin switch that turns the brakes ‘ON’ if the trailer does disconnect.  The switch has a cable that attaches — one end to the tow vehicle, and the other end to the switch — so if the trailer gets too far away from the tow vehicle, it pulls the pin to ‘Flip’ the switch.  Here’s a quick unboxing video to show the parts and give a little more explanation.

OK, that’s the quick overview of the parts.  In reality, the pin pull switch and the cable (which connects the pin to the tow vehicle) are the critical parts.  Pulling the pin connects the battery to the trailer brakes.  So, mounting those parts properly, and connecting them for each trip is critical.  Here’s another image to see the parts.

Trailer Breakaway Kit
Image of the Hopkins Trailer Breakaway Kit with Battery, Pin Switch and Cable.

The battery on the trailer needs power to keep it charged, so it does wire into the trailer electrical system.  If something bad happens and the trailer comes loose, pulling the pin connects the battery to the trailer brakes to hopefully avert disaster.  That’s really it.  The battery in the trailer breakaway kit doesn’t do anything else.

Wiring Up Your Trailer Breakaway Kit

Here is a wiring diagram for your Trailer Breakaway Kit.  This is typical, but check your system to be sure the wires (colors) are the same.  This little bit of schematic attaches into the full trailer wiring diagram from our other article.

Power to charge the battery comes from the “Aux +12V Power” wire (Usually Red, but sometimes black).  The white wire is “Ground” or “Common”, then blue is the “Brake” wire.  The Red comes in to charge the battery, the Blue powers the brakes if the pull-pin yanks out.  The White provides a return, or ground path for both the battery charger and the brakes.

Breakaway Wiring Diagram

These are all available with a 7-Pin vehicle connector — which is very standard.  Such connectors are often built-in stock on pickup trucks and large SUV’s intended for pulling a trailer.  You can find a lot more information about connectors and what the wires are for on our Trailer Wiring Diagram page.  Also, for the full picture, superimpose this image over the Trailer Wiring Diagrams on that page.

We suggest a 7-wire system so you have all the right connections.  However, If your system has only a 5 wire plug, you can (in a pinch) wire the breakaway battery charger into the brown “Taillights and Running Lights” wire (instead of the Red) — then always drive with your lights on.  (There are a lot of good arguments for having your lights on when you’re driving anyway.)

Finally, wire it up using tips from the Trailer Lights and Wiring article.

Making Sure It Works

It’s really pretty simple to see that it works.  Once you have it all wired in, simply jack up one side of the trailer, and spin the tire.  It should spin freely if the pin is “IN”.  Pull the breakaway switch Pin out, and the wheel should stop and hold solid.

Specifications say the system must hold the brakes for 15 minutes, so if you’re testing, let it sit for a bit to see.  It’s really a matter of battery size and current draw.  If you have a single axle trailer, it should be no problem for most trailer breakaway kit.  Tandems draw more, but are usually OK in the standard size.  Triple axles often need a larger battery.


So, where do you connect the trailer Breakaway Kit switch cable?  It attaches to the pull pin on one end, and to the vehicle on the other.  The connection to the pull pin should be semi-permanent — and usually the kit gives you the cable with the pin already attached.  Then, on the vehicle end, use a secure connection like a locking carabiner or screw chain link.  The connection does not have to be super strong, but it does have to be secure.

Now, where does it mount?  This image from RVUpgrades.com shows both the traditional cable, and a coiled upgrade.  It also shows the pull pin switch and how the cable attaches at the hitch on the tow vehicle.  In this case, it’s just clipping a carabiner at the same location as the safety chain.

Coiled Cable Connection

The coil is nice for a clean look, but it does not address issues of cable length.  They made this image to look bad for the cable because they want to sell you the coiled cable, but if you look past that, it does illustrate the concepts.

The image above shows a reasonable position for mounting the breakaway switch, but I normally like mine a little higher so it does not interfere or tangle with the safety chains.  If chains are correct, it’s usually not a problem, but mounting the switch above the chains does help.  The image above is missing the safety chains, so the coiled cable application is not actually as clean as it looks.  Also, when a side mount tongue jack is there, it’s often a good idea to put the breakaway switch on the other side from the jack — just so they don’t tangle with each other.

Why Have A Trailer Breakaway Kit?

Let’s get into some meat.  If you think about the trailer breakaway kit very long, some important questions arise.  This is a tough issue, so here we go.

First, we have to ask:  When would you actually use the breakaway function?  Yes, when the trailer comes disconnected, but don’t we have safety chains for that?  If the safety chains are on correct, then what’s the point of the trailer breakaway kit?

The most likely time for an issue comes when the hitch was not on correctly.  Yes, it happens, and usually it’s human error.  For instance, not properly attaching the hitch.  Anyway, . . . so the hitch bounces off, but the safety chains are there?  Though it’s a scary situation, applying the brakes brings it to a stop (because the trailer is still connects with safety chains and electrical.)

For the breakaway kit to have value, someone must fumble the hitch as well as forget the safety chains.  But, I always connect the breakaway cable last.  That means if I am distracted from connecting the safety chains, I’d also forget the breakaway cable, rendering it useless.  Right?

From a good design standpoint, we already have both belts and suspenders with a good hitch and safety chains.  Those will handle potential troubles for good trailers with good construction.  But, what about the other situations.  What about folks that don’t properly care for a trailer?

A Case For The Breakaway Kit

OK, let’s look at this case.  If someone fumbled the hitch (not uncommon);  AND the safety chains are too long (very common);  AND the safety chains are not sufficiently strong (also common);  THEN if the hitch bounces off, and the tongue hits the ground to dig in, the high forces can break the chains.  With safety chains broken, the trailer is free, and the trailer breakaway kit comes into action.

Is that an unreasonable scenario?  Maybe not.  It’s not uncommon for safety chains to be light duty — too light for the situation.  It’s not unusual for the safety chain connections to be just a simple hook (great for light trailers, but not for big ones).  How many times have we seen chain welded directly to the trailer frame?  Welding seriously weakens an otherwise strong chain.  Or how about twisted safety chains (read the article).  And, how about chains that are thin from grinding and dragging on the ground.  You’ve seen them, sparks dancing as they roll down the road.  Finally, if safety chains attach under the tongue, and the tongue drags the ground, it can pretty quickly grind off the attachment, then the trailer is loose.  All of these contribute to a situation where the trailer breakaway kit can have a purpose.

I’m sure there are other scenarios, but that’s the best I can come up with.  Yes, this is a “protect us from the idiots” law, so I’ll do it — especially since I see so many neglected trailers.  For that matter, I’m not immune to being the idiot — I’ve done my share of oops.

If you have better info about the use of breakaway kits, please comment below.

Getting The Right Proportions

So, what are the right proportions for a trailer breakaway kit cable when comparing to the other items?  Of course, the hitch is the solid point we compare to.  If the trailer comes off the hitch, the safety chains must come tight next.  That must happen for the trailer moving back as well as forward (when the tongue goes under the tow vehicle).  The electrical connection must be longer than the chains so it stays connected — allowing use of trailer lights and brakes.

If the chains come off or break, you want the breakaway pin to pull quickly.  I don’t think it matters if the electrical connection or the breakaway cable pull next.  At this point the trailer is on it’s own, so we just want it to stop.

* There is a good argument for having the breakaway cable shorter than the safety chains.  It means the trailer brakes come on before the safety chains disconnect (or snap or whatever).  That’s a reasonable thing, especially if you are going downhill.  This does solve one interesting problem.  If a trailer hitch comes off and the trailer is tethered by safety chains, when you apply brakes, the trailer can potentially hit the tow vehicle.  Maybe even as the tongue dives under the vehicle.  Depending on your trailer brake balance, applying the vehicle brakes (assuming the electrical is still connected), may or may not make the trailer want to slow more than the tow vehicle.  Having the trailer breakaway kit start that job before the safety chains are also gone, can be a benefit.

I’ll let you decide which way to connect things.  The above just gives some things to think about as you make that decision.

Good Luck With Your Trailer Breakaway Kit

If you don’t have a breakaway system, check to see if you need it in your location, for your size of trailer.  They are not that hard to put in, but it is one more thing you need to maintain.  Hopefully, you’ll never need it.

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