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Ken O'Neill avatar image
Ken O'Neill asked

Problem with DC-DC charger installation

I have installed an Orion isolated DC-DC charger 12v-12v 18A. I wired the positive (black) and negative (white) wires from the 7-pin to the input side of the charger. Then I wired the output side to the battery via the positive and negative busbars. See attached diagram. The truck has 10 ga wire with a 30A fuse to the 7- pin. With the trailer connected to the 7 pin but not attached to the truck hitch, the charger is working and putting about 17 A into the batteries. However the trailer running lights and turn signals are not working.

I presume that is because the white (negative) 7 pin wire is now connected to the input side of the charger and I have interrupted the circuit for the trailer running lights. (Perhaps I should have gotten a non-isolated charger...)
But now what? I don't want to rely on the hitch to create a negative contact between trailer and the truck. Can I connect both the negative input and output sides of the isolated charger to the negative bus and also reattach the white (negative) 7 pin wire to the negative busbar?

Charger wiring diagram.pdf

installationorion dc-dc
charger-wiring-diagram.pdf (112.6 KiB)
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Bob K avatar image Bob K commented ·

You need to reconnect both wires to the 7-pin connector. The trailer needs both of them to run various DC functions while you're towing.


The DC charger is supposed to have its own dedicated wires from your truck battery or alternator, and the isolated charger is the correct style for those of us with trailers so that the ground to the tow vehicle is made through a wire rather than through the hitch. However, if you wanted to try to power the DC charger off of the wires on your 7-pin connector (not recommended since they're small gauge wires), then you would have to pigtail off of the +12V and GND wires to the input side of the charger. The output side + and - would go to the + and - busbars within your trailer.

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Kevin Windrem avatar image
Kevin Windrem answered ·

The negative wire from the 7-pin must be connected to the trailer chassis. It can also go to the negative input of the Orion. The Orion output connects to house DC electrical system as you have described and will at some point also connect to the trailer's chassis. That's all OK.

10 gauge in the truck is a bit small. I had 12 gauge in my truck and replaced it with #6 and used the truck chassis for the negative. I used the trailer chassis for the negative and ran #6 for the positive and get close to the 18 amps of charging current.

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