Does trailer draw power from truck - Chevy and GMC Duramax Diesel Forum
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post #1 of 20 (permalink) Old 03-12-2011, 07:34 PM Thread Starter
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Does trailer draw power from truck

I sometimes camp without hookups. I alway unplug the trailer thinking if the furnace runs the camper battery down, it might drain the truck battieries.

A friend has another brand truck and says there is a relay that wont let that happen, just would like to know if that is the same with the Druramax.

If I leave it plugged in, does it pull power if the truck is not running? Thanks.

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post #2 of 20 (permalink) Old 03-12-2011, 07:44 PM
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all the campers that i'm aware of, the power in the camper is completely seperate from the truck. i have a 5er and used to use 2 batteries for the camper lights while camping, i finially upgraded to a small generator last year so we could run the entire camper.

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post #3 of 20 (permalink) Old 03-12-2011, 08:16 PM
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It depends on how it is wired in, I have dump trailer and it charges the battery from the truck and gives power all the time if it is plugged in. You really want to test it out. You would need a voltmeter to see if charging voltage goes to your camper when the truck is running.

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post #4 of 20 (permalink) Old 03-13-2011, 04:44 AM
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I'm thinking it does, but can't remember. Mines on a switch so I know when there's juice back there and when there's not. Like stated, just put a test light on the trailer plug on the back of truck.

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post #5 of 20 (permalink) Old 03-13-2011, 06:24 AM Thread Starter
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I know the truck charges the trailer when the truck is running, I found the charging pin on the plug's socket and it wasn't when I got the truck. The dealer fixed it, they said it had a blank fuse in the fuse box from the factory. They just had to replace it with a real fuse. It charges nicely when running.

My question is if there is any protection from discharging the trucks battery completly if its not running. My friend has a Ford and says his has a relay that cuts power to the truck when its not running to prevent that. Just want to know if Chevy does the same thing.

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post #6 of 20 (permalink) Old 03-13-2011, 06:37 AM
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The 12v feed to the trailer is live 24/7 so yes it will run down the truck batteries if left connected. It is posible to add a relay so this cannot happen.

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post #7 of 20 (permalink) Old 03-13-2011, 06:46 AM
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Unhook it to be safe. The truck charges the batter for the emergency disconnect....

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post #8 of 20 (permalink) Old 03-13-2011, 05:02 PM
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Yep, it's a live 40a continuous draw. I did see a mention some time back that there were plans, on newer models, to smarten up the trailer feed for your protection from rundowns. When the trucks’ batteries dropped below a certain level, it drops the trailer feed, like the doom/cargo/radio does now.

If you’re boon-docking and need the additional power from the truck to extend your stay, just unhook the negative from the passenger side battery. You only need one battery to start the truck, and you’ll keep that one in reserve in case of the other drops out.

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post #9 of 20 (permalink) Old 03-14-2011, 11:12 AM
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On my 2008 the trailer power connection is live all of the time. However, but IIRC the starting battery is only used to start the truck and is isolated from the rest of the truck with a diode.

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post #10 of 20 (permalink) Old 03-14-2011, 11:21 AM
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The Duramax uses both batteries all the time-- Starting [takes lots of amps] and running. They are wired in parallel. There is no diode in the system.

The trailer terminal is hot all the time, if the wire has been connected, and it has a fuse in the under hood fuse box.

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