Friday, December 9, 2022


RV Doctor: Trailer breakaway switch and inverter questions


Dear Gary,
I have several questions about the breakaway switch on a travel trailer. First, thank you so much for all of your time at the Hershey RV Shows. You always go way beyond what is expected to answer questions. My wife, Jayme, and I have attended several of your sessions over the years. I have always learned something from each session, even when I attended the same session two days in a row!

Now for the questions concerning a breakaway switch on a travel trailer. Is the power to the brakes directly from the battery or is it routed through the converter distribution box? Should a travel trailer be stored with the pin in or out of the breakaway switch? With the breakaway pin out, do the switch and the brakes consume much power from the battery? If you have the ability to keep the batteries charged during storage, should you remove the breakaway pin? Is it best for the trailer brakes to be set (pin out) or open (pin in) during a month or more of storage?

Also, I had an inverter installed with an automatic transfer switch so that all of the 120V outlets and systems will work in the trailer. It is not powerful enough to run the microwave or air conditioner, but can power anything else in the trailer. Besides using the TV while boondocking, my main use is so I can run the absorption refrigerator using electric during travel. I have to engage the battery disconnect switch before I turn on the inverter and keep it disconnected while the inverter is on. If I have the inverter on and the battery disconnect switch engaged during travel, will this affect the operation of my breakaway switch?

Thanks for your help in understanding the breakaway switch and the impact on the batteries and brakes. —Graham and Jayme M.

Dear Graham and Jayme,
It was good to have you at the seminars in Hershey!

The breakaway switch on a towable RV is always powered by the battery bank on the trailer. That way, if the tow vehicle and trailer ever part company, the brakes will be activated and remain fully applied. It should not be connected through the converter since the converter is only activated with the application of 120-volt AC power.

Always leave the pin in the switch. Once a year, jack up one or two tires on each axle, spin the tires and pull the pin to be sure the brakes are fully activated. The tire/wheel assembly should immediately stop with the pin pulled.

While the pin is out, spray electrical contact cleaner inside the switch housing to keep those contacts fresh, then fully reinsert the pin. When the pin is out or not fully inserted, the brake magnets will continue to draw power and eventually drain the battery bank. The brakes can draw a lot of current – upwards of 3 amps or so for each magnet, depending on the size of the brakes. So the bottom line is never remove the pin except once a year for cleaning and testing.

While driving, you’ll want the alternator of the tow vehicle engine to keep charging the battery bank on the trailer. If you disconnect the battery, it won’t be able to accept that charge. I’m not sure why you need to disconnect the battery to activate the inverter while traveling. You should be able charge the battery while driving AND operate the inverter to power the AC side of the refrigerator. In this manner, nothing will affect the breakaway switch. Even with the disconnect activated, the breakaway switch should still be able to power the brakes in an emergency. Easy to test – activate the disconnect switch, spin the tires and pull the pin. You might need to have your tow wiring evaluated.

Besides using the inverter, you could also run the refrigerator to get it cold overnight, and turn the whole refrigerator off while driving. Without opening the door often, the contents will typically stay cold enough as you drive. Once you stop, light it on propane, turn on the inverter, or plug into shore power. A couple different options to consider.

gary-736Read more from Gary Bunzer at the See Gary’s videos about RV repair and maintenance.


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2 years ago

Dear Gary, Maybe I’m missing something but I need some help. I have a class C motorhome and want to flat tow my Jeep. The setup I am looking at recommends a break away brake system. This is basically a cable running from the brake pedal on the jeep to the frame of the RV which engages the jeep’s brakes if it breaks away from the towbar. This doesn’t seem like it would be easy to disconnect in order to actually drive the jeep around once we get somewhere. How do you actually do that?

2 years ago

Got stopped once in a holiday trailer “safety blitz” where the RCMP officer made me pull the break away switch on my fifth wheel and try and drive away. Every thing worked but I make sure I check it every year now. I also adjust my brakes every year so the break away can put the brakes on to the max.
I also heard of a guy whose switch got pulled accidentally while going through some rough terrain boon docking. He couldn’t figure out why his trailer batteries kept going dead until somebody noticed the switch out. He did say that the trailer did seem to pulling awfully hard the last little bit before parking.

charles Yaker
2 years ago

Ever notice that the break away switch only works when trailer hitch comes open and trailer is left behind not if in an accident trailer hitch breaks and trailer heads for the cab. I realize small odds but just saying.

2 years ago
Reply to  charles Yaker

Other systems are utilized (and usually required) for normal stopping. If the hitch ‘breaks’, well you have a whole different set of ‘idiot optics’ in play.

2 years ago

Had the pin pull out of our 42′ rig while driving. The cable got tangled with other objects in the bed of the pickup…Could not even tell it was pulled. We have hydraulic brakes. This has happened twice.

I have since checked to see if the tires spin by diving in coast speed and pulling the pin. The truck/trailer still stops (slowly) but I question the braking ability of that configuration.

Is it that the wiring may be too small?

Is there a setting on the hydraulic braking device?

I can use the brake controller and the brakes work just fine. I have it set at 7 out of 10. This seems to be isolated to just that emergency brake setup.

Any suggestions from anyone would be appreciated. I can research this but I have had to work on too many other things and have not gotten back to this just yet.

Charles Yaker
2 years ago
Reply to  TravelingMan

did you check your fluid level also break away on my rig has it’s own activating battery this may need replacement it should be located near the hydraulics in a small 5 x 5 box with green yellow and red lights on it

2 years ago
Reply to  TravelingMan

Typically hydraulic trailer brakes use a ‘surge’ system to apply trailer brakes during braking. If yours has an electrically operated hydraulic system, you would need to read the manual or take it in… someplace. :-/ I have never seen one. It requires its own battery mounted on the trailer to apply the brakes if it ever separated from the tow vehicle, that is where the pin switch comes in.

Stay cool

2 years ago

Like Gary says, always leave the Pin in the switch!

A long time ago, someone told me to remove the pin when I was parked and it would activate the brakes and keep the RV from ROLLING! NEVER, EVER Do this! By removing the Pin and leaving it out, the BRAKE AWAY Switch will Overheat and most likely Melt and short out!

So, except to test the circuit on your RV, Leave the Pin in the Brake Away switch!