Adding a Battery to a Snowmobile Trailer for Interior Trailer Lights

Updated 05/29/2020 | Published 09/07/2011

Products Featured in This Question

Hopkins 7-Way RV Style Connector with Molded Cable - Trailer End - 8' Long - RV Standard

(908)

$46.90

Snap-Top Battery Box with Strap for Group 24 to Group 31 Batteries - Vented

(260)

$19.44

Replacement Mini-Rocker Switch for Ventline Ventadome Trailer Roof Vents

(31)

$15.96

Question:

Hi, I have an enclosed snowmobile trailer w/electric brakes and inside lights. I would like to add a battery to turn on lights when not connected to my truck. What is the best way to do this? thanks

asked by: Brent

Expert Reply:

Start with mounting a battery. Since the trailer is enclosed, it would be a good idea to mount it on the trailer frame using a battery box like # 329-HM318BKS. Next, you will need to have the right kind of connectors on the truck and trailer. I would use a 7-Way RV style if you do not already have them on the truck and trailer.

There is a 12 volt circuit on a 7-Way. You can run a wire from the 12 volt circuit on the trailer side connector to the positive battery terminal. The battery should be grounded to the trailer frame. The 12 volt hot lead will maintain the trailer battery, though it will not be able to fully charge it.

With the battery installed, you will want to wire the lights to it. The lights will have a power wire and a ground. The power wires for the lights is currently connected to the 12 volt circuit from the trailer connector. You will need to instead route the trailer light power wires to a switch, like # BL0108-00, using a spade terminal. Using another spade terminal, connect a length of wire to the positive battery terminal. Hit the switch and the lights will turn on, running off of the trailer battery. They will no longer come on when connected to the truck via the 7-Way connector because the lights cannot have 2 power sources.

expert reply by: Michael H

Shane C.

5/24/2020

If I’m using a junction box for lol the connections, do I run a wire from + on the battery to the junction box where the 12v acc wire, 12v circuit from 7-way, and black 12v wire from electric brakes are connected? Should I add a fuse to any of those circuits? I’m curious if there’s any problem with the electric brakes breakaway kit battery and the trailer battery battery being connected together. Or the interior lights being powered by the battery and 12v circuit from 7-way. Thanks for the help.

Chris R.

5/27/2020

Yes, you will connect the 12V wire from your aux battery to the same 12V post in the junction box that you have the 7-Way's 12V wire attached to. This circuit should already be protected on the vehicle side - so an additional fuse isn't needed.

Shane C.

5/27/2020

@ChrisR Thank you for the reply. I did what you said. Everything works, however the “charge” light on my Hopkins Breakaway #20099 stays illuminated. I found on your site where it’s advised to install the Roadmaster one way park light diode on the 12v acc battery + line. So I did that and the charge light goes off, but now my interior lights do not work. This is without the vehicle connected. I thought about wiring the aux battery and interior lights to their own post in the junction box, but I want the aux battery to charge from the vehicle when hooked up. Any recommendations?