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Old 04-15-2016, 09:59 AM   #1
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Power to the trailer plug on my GMC

I have a 2009 GMC 3500 Duramax and pull a 2005 Cardinal fifth wheel,33LE. I can't seem to find which pin is "hot" coming out of my factory installed 7 pin connector. I've been towing this RV for several years and just "assumed" that the truck was trickle charging my RV battery while I was on the road. I have only done single night boondocking on the way to campgrounds so my battery may have been fully charged from being connected to shore power at home before leaving and then being recharged upon arrival at the campground and plugging back in to shore power. Will be traveling out west all summer and will probably be spending some nights not in campgrounds. I do have a generator just in case.

I know I won't get much power back to my RV when traveling but every little bit helps. Thanks in advance for any info. I've been visiting the forum for several years and received much info for a newbie. Now I'm just a better informed newbie.

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Old 04-15-2016, 10:31 AM   #2
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Some Chevy and GMC trucks have power to their 7-pin trailer connection all the time, while other require the vehicle to be running. My Ford only supplies power when the truck is running.

Many trucks are missing a relay and fuse (found under the hood). You'll have to investigate your truck for the answer.

Check pin 1 to pin 4 on your truck's 7-pin connection with a volt meter or 12V test light.
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Old 04-15-2016, 10:32 AM   #3
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If you look at your plug i think it is the first one from the top at like the 1 o'clock position at least that is how my 2013 GMC is wired
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Old 04-15-2016, 10:43 AM   #4
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On My 08 Silverado there needed to be a wire hooked up in engine compartment fuse box and a fuse installed.
Wire is not hot when truck is off.

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Old 04-15-2016, 10:45 AM   #5
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On my '14 Silverado a plug had to be connected to the battery. Once that was done, the battery on the TT was getting charged. It's a small wire that was zip tied to a hose near the battery. It was gray
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Old 04-15-2016, 11:49 AM   #6
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Wire needs to be connected may also need fuze added most GM products are hot all the time
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Old 04-15-2016, 12:13 PM   #7
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Depending on the year, but my 2005 Duramax was wired with trailering package, but had a blank in the fuse slot under the hood for the 12v power. Just had to buy a large 50amp fuse and it was good to go.
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Old 04-15-2016, 12:29 PM   #8
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Same with my GMC. I believe it is now hot all the time.
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Old 04-15-2016, 01:26 PM   #9
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I can't say enough good about the guys who hooked my system up for me. They specifically told me they tested the 12v hot line to be sure it was connected and if not, they would have hooked it up. I did find out after the fact that my Titan does not provide power when engine is not running though.
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Old 04-15-2016, 01:55 PM   #10
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I had the same issue with my 2012 Yukon The wire is taped up by the fire wall under the hood. It is red you need to open the fuse box under the hood and hook it up. The fuse (on mine is a 40amp) was already in place all I had to do is buy a metric nut and hook it up. I also found out that if you push the tow haul button while the engine is running it will boost the current to the TT battery.

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power, trailer

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