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Should an Electric Trailer Jack Run Off of a Trailer Breakaway Battery

Question:

I just purchased a used 24foot interstate cargo trailer. It has a break away battery and a automotive style battery inside trailer to run work lights. I noticed the electric trailer jack runs off the break away battery, when I disconnect the large battery inside the jack still works. Are the two batterys in series or parallel? I would like they should be separate circuits. Where can I find a wiring diagram showing from the tow vehicle to the rear lights of the trailer and everything in between.

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Expert Reply:

The trailer jack should very much NOT be powered by the breakaway battery. That was likely done by the previous owner for convenience. The breakaway battery is a dedicated battery for the breakaway system only. It needs to be able to apply the trailer brakes on full for 15 minutes.

If the jack was to run down the battery then the breakaway system would not be able to power the brakes for long enough.

Also, a breakaway battery is too small for the power needs of a jack. Most breakaway batteries are only rated for around 5 amp hours.

As far as a wiring diagram for your specific trailer the only place that would have that is the trailer manufacturer and it isn't likely they would have it. But there are only so many circuits a trailer uses so you can follow the generic wiring diagram I have included. Keep in mind that there is no wiring color code standard and the colors used are common but not standard.

A good way to keep trailer wiring neat and organized is to use a junction box such as # 38656. I have linked a video showing an example installation for you.

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