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 is a legal requirement in many jurisdictions. It is 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 have seen how terrible this is – and even more terrible – it is not that uncommon for a trailer to unhook.  People forget to tighten the hitch, or don’t get it on totally.  Either way, that is 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 is 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 is a quick unboxing video to show the parts and give a little more explanation.

OK, that is 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 is 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 is really it.  The battery in the trailer breakaway kit does not 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 “Brakes” 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 SUVs 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 are driving anyway.)

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

Making Sure It Works

It is 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 are testing, let it sit for a bit to see.  It is really a matter of battery size and current draw.  If you have a single axle trailer, it should be no problem for most with a typical trailer breakaway kit.  Tandems draw more, but are usually OK in the standard size kit.  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 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 is 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 coil, 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 is 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 is 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 is 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 is human error.  For instance, not properly attaching the hitch.  Anyway, . . . so the hitch bounces off, but the safety chains are there?  Though it is a scary situation, applying the brakes brings it to a stop (because the trailer still connects with safety chains and hopefully the electrical.)

For the breakaway kit to have value, someone must fumble the hitch as well as forget the safety chains.  Or is it?  But, I always connect the breakaway cable last.  That means if I am distracted from connecting the safety chains, I will 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?  Or is there something else that makes the kit valuable?

A Case For The Breakaway Kit

OK, we can 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 is not uncommon for safety chains to be light duty – too light for the situation.  It is 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 have 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.

A Case Closer To Home

Crash with no Breakaway KitStarting in a similar manner as above.  If someone fumbled the hitch (not uncommon);  THEN the hitch bounces off, how do they stop the trailer that is dragging behind them still attached to the perfectly good safety chains?  This scenario is much more likely, and it does not have all the caveats of the case above.

This kind of thing happens.  If the pin switch cable is short enough (a little shorter than the trailer safety chains), then the breakaway kit puts the trailer brakes on, and you can bring the tow vehicle to a stop without the trailer smashing into the car.

On the other hand, if the cable is too long (like the image above), then the trailer breakaway kit is just a passenger, and cannot help in the moment of distress.

That is a more practical case, and that one can happen to any of us.

Moving Forward

I am sure there are other scenarios, too.  Yes, many people think of it as a “protect us from the idiots” law, but if we arrange it right, it can help us too.  For that matter, I am not immune to being the idiot – Heaven knows I have 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 comparing to other items?  These things connect the trailer:

  1. The Hitch.  A solid point, and this is the baseline.
  2. Safety Chains.  If the trailer comes off the hitch, then safety chains are next.  We want trailer safety chains as short as practical.
  3. Electrical Connection.  Wires should be longer than the chains so lights and brakes can still actuate if the hitch comes off.
  4. Where in this order should the Breakaway Switch pull?

I have heard different opinions, but more important, many setups are haphazard.  If the chains come off or break, of course, we want the breakaway pin to pull quickly.  If the trailer is on it is own, we just want it to stop!  But, what if the hitch comes loose and the chains don’t break or come off?

There are good reasons to make 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 is good, especially going downhill.  This solves one problem.  If the hitch comes off and the trailer is only on by safety chains, when you apply vehicle brakes, the trailer will hit the tow vehicle.  The tongue may hit (like this image), or it may dive under.  Depending on your brake balance, applying the vehicle brakes (assuming the electrical connection?), the trailer may or may not slow more than the tow vehicle.  Having the trailer breakaway kit start the job before the safety chains also shred is a big benefit.

I will let you decide.  The above is something to think about as you make the decision.  Whatever you decide, make it deliberate, and make sure it will always work for you.

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 will never need it.

On the other hand, if you do need it, suddenly it is priceless.

Next up, read about Mixing Tandem Axle Brakes.


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