Switch and relay on 12v trailer backup light circuit


Old 01-06-18, 07:02 PM
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Lightbulb Switch and relay on 12v trailer backup light circuit

Hello, In my trailer I want to install rear lights that are simply switch activated to run off the trailer battery, but also have them come on as reverse lights when the tow vehicle is in reverse. Can I just wire a wall switch in parallel with the load side of a relay, and then run the switch side of the relay to the tow vehicle's reverse signal? See my excellent drawing attached.

Does this sound safe and reasonable? Any better way?

Thanks in advance.
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Old 01-06-18, 09:00 PM
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That looks sensible and would be exactly how I'd wire it. This is assuming these lights aren't monster sized or anything. Do you know yet how many amps total they will be drawing?

I personally would not use an AC wall switch. It will work, but the contacts will become pitted over time, and then there is the resistance issue. I suppose if it's in an easily-accessible location and you don't mind replacing it eventually, not much harm. Make sure you don't exceed the DC amperage rating for the switch. If this switch is going to be exposed to the elements you've got that to worry about. They make lots of nifty 12 VDC switches which are made for the purpose and take up far less real estate and are easier to mount, so I'd use one of those.
Old 01-06-18, 09:28 PM
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Welcome to the forums.

core pretty much summed everything up.
I'd just add two things. Once you've determine the amperage of your lights install a fuse and fuseholder at the battery to protect your wiring in case of any shorts. Try to go with LED type lights as they'll use a lot less power from the battery.
Old 01-06-18, 10:46 PM
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Thanks for your second opinions. Great to hear I'm on the right track.

I will be using a 12v rocker switch as part of a panel kit to control these from the trailer wall. The lights themselves are 36W total or 3A, so I will probably use a 5A fuse.

All the LED choices these days are fantastic. These lights have six 3W Cree LEDs each and I will have two for under $20. Anything I might back into will just turn to dust as soon as I turn the lights on!

Thanks again.

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