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Open Roads Forum  >  Towing

 > Explain how emergency trailer brake gets power?

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ewarnerusa

Helena, Montana

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Posted: 05/12/22 01:01pm Link  |  Quote  |  Print  |  Notify Moderator

I recently did some battery wiring maintenance on my TT and it occurred to me that I don't see where the emergency trailer brake gets its power. I mean the emergency pin that gets pulled out should you have a trailer separate from the tow vehicle that should energize the trailer brakes. I had suspected that there should be a direct connection to the battery, but the only OEM connection was to a circuit breaker on the tongue which feeds the electric jack and the main 12V to/from the main power center. Does the emergency trailer brake get power from the main power center?


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MNRon

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Posted: 05/12/22 01:26pm Link  |  Quote  |  Print  |  Notify Moderator

Pretty sure that emergency trailer brakes are direct connected to the battery through the break-away switch; no fuses, no breakers, no other switches etc. If you pull the break-away pin they should supply full battery power to the brakes.


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valhalla360

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Posted: 05/12/22 01:59pm Link  |  Quote  |  Print  |  Notify Moderator

Unless someone rewired it...should be direct from the battery to the breakaway switch and then on to the brake magnets.


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BB_TX

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Posted: 05/12/22 02:07pm Link  |  Quote  |  Print  |  Notify Moderator

Agree with above. You should always be able to measure +12 vdc on one side of the breakaway switch. If not something is wrong.

ewarnerusa

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Posted: 05/12/22 02:15pm Link  |  Quote  |  Print  |  Notify Moderator

I bought the camper new from dealer and the only rewiring would have been by me. I'll have to do some testing to see what happens. If I remember right, the wire from the back of the breakaway switch went back into the junction box on the frame where the main 12V supply to converter/power center.
I found a photo I took for another purpose which I've zoomed in and cropped down.
I think the gray wire(s) are from the breakaway switch.
[image]

BurbMan

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Posted: 05/12/22 02:33pm Link  |  Quote  |  Print  |  Notify Moderator

That connection is inside the junction box where your 7-pin cord terminates at the trailer. The breakaway switch is wired to both 12v positive from the TT battery and the blue brake wire.

Reisender

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Posted: 05/12/22 03:05pm Link  |  Quote  |  Print  |  Notify Moderator

Best way to test it is to hook up as per normal. Then disconnect your 7 pin, pull the emergency tether and then roll forward. If you are dragging your wheels you are good to go. Don’t forget to reinsert the thingy. We do this every 6 or 7 hookups...just in case. [emoticon]

ewarnerusa

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Posted: 05/12/22 03:35pm Link  |  Quote  |  Print  |  Notify Moderator

BurbMan wrote:

That connection is inside the junction box where your 7-pin cord terminates at the trailer. The breakaway switch is wired to both 12v positive from the TT battery and the blue brake wire.

Thank you, this seems to correspond with what I'm remembering and what is in the picture. I'm pretty sure the 7-pin cord comes into the bottom of that junction box where the sun-baked red 12V wire from the circuit breaker is entering from the side. One or both of the other small gauge wires are coming from the back of the breakaway pin box if memory serves. I'm trying to remember all of this as I sit in the office and the camper is at home. I'll go check some things out when I'm hom.

* This post was edited 05/12/22 09:43pm by ewarnerusa *

ewarnerusa

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Posted: 05/12/22 06:01pm Link  |  Quote  |  Print  |  Notify Moderator

Okay I was able to confirm that the two wires going into the side of the junction box along with the main 12 volt do come from the breakaway switch controller. When I pull the pin from the breakaway switch, I observe about a 7 amp draw on the batteries. So things seem to be working as designed.

toedtoes

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Posted: 05/12/22 08:24pm Link  |  Quote  |  Print  |  Notify Moderator

My trailer has both a house battery and a hitch battery (to power the hitch jack). The trailer brakes are connected to the hitch battery.


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