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Discussion Starter · #1 ·
I'm looking for a 12V power source near the back end of the truck for a low-amperage use. Looking at trailer wiring harness diagrams, I see that a seven pin harness has a pin, usually wired black, that is described as 12V Battery.

Does this pin have power normally on these trucks? If so, does it have power when the ignition is off, or only when on?

I want to add some lighting inside of my canopy, and to add a backup camera. If there is 12V to this pin all of the time I could add both, but if it only has power when the ignition is on then it would only be good for the backup camera.

Thanks.
 

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That would be a good place to tap into 12 volts, depending upon whether it is "always hot" or a switched wire, which was your question.

Rather than guess or rely on a yokel like me, take five minutes and test it. Four minutes will be finding your under $20 digital multimeter, one minute to test. Turn on ignition switch, get positive test for power to that connector; then turn off ignition switch and you'll know.

You may need to run a dedicated "switched" wire for this from the fuse box.

My edjamacated guess is that the connection is "always hot", typically used for auxiliary lighting inside a trailer.
 

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Discussion Starter · #3 ·
I haven't tested it yet because my truck lacks the three relays under the kick-panel and lacks the pigtail harness from the on-frame connector at the back. My assumption is I'll have to get those parts eventually, but if anyone had prior experience figured it would be useful to others to know too.
 

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I haven't tested it yet because my truck lacks the three relays under the kick-panel and lacks the pigtail harness from the on-frame connector at the back. My assumption is I'll have to get those parts eventually, but if anyone had prior experience figured it would be useful to others to know too.
I wont be home for a few more weeks so I could test it for sure then. My guess is that it is always hot. I have a camper and am on a popup portal. There are a few threads on this, running your 12V fridge while towing. The 12V power from the 7 pin is designed to maintain or charge your trailer battery while towing, if you're running a 12V accessory like a fridge while towing and stop for a prolonged time with the trailer connected the the 7pin on the tow vehicle it "can" deplete the tow vehicle battery.
 

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Discussion Starter · #5 · (Edited)
Well, I was bored last night so I went through the incredibly hard to interpret factory wiring diagrams from the FSM and made a new drawing that I think describes the wiring from the bulkhead connector to the back.

It looks like it is 12V constant to that pin. It arrives on Pin 2 (violet) on Connector C52. Pin 1 on that connector is the trailer brakes signal.

If anyone needs it, the diagram is attached:



Note, the trailer wiring from C125 and C150 onwards doesn't seem to make a lot of sense to me, unless the pin arrangement on the backside of the 7 pin adapter has some internal rewiring when it gets to the trailer-facing side. I made the diagram by starting with the functions from before they exit the cab at Connector C1. Hopefully it's accurate.
 

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Discussion Starter · #7 ·
i need a diagram like that for a 2006 i don't have a purple wire in my harness going to the 7 way plug
You certain of that? Connectors C51 and C52 are on the frame on the left side in from behind the bumper. Basically there are three connectors in that rough area, and these two are the ones that then take a pigtail connector that goes out to the trailer plug on the hitch.
 

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Well, I was bored last night so I went through the incredibly hard to interpret factory wiring diagrams from the FSM and made a new drawing that I think describes the wiring from the bulkhead connector to the back.

It looks like it is 12V constant to that pin. It arrives on Pin 2 (violet) on Connector C52. Pin 1 on that connector is the trailer brakes signal.

If anyone needs it, the diagram is attached:



Note, the trailer wiring from C125 and C150 onwards doesn't seem to make a lot of sense to me, unless the pin arrangement on the backside of the 7 pin adapter has some internal rewiring when it gets to the trailer-facing side. I made the diagram by starting with the functions from before they exit the cab at Connector C1. Hopefully it's accurate.
I know this is an old post but hoping you can help out. I had the same idea but found out trailer plug is only hot when truck running. If i chase back wires is there a hot under the spare tire or do you have to go all the way to cab or battery to get steady power?
 

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Discussion Starter · #9 ·
I know this is an old post but hoping you can help out. I had the same idea but found out trailer plug is only hot when truck running. If i chase back wires is there a hot under the spare tire or do you have to go all the way to cab or battery to get steady power?
I am not aware of any. There's not a lot of wiring behind the cab as the ABS sensors, speed sensor(?), lights, fuel pump, and backup camera and sensors are the only things back there.

I'm looking at wiring-in for a winch, I'm planning on running new cable from the battery.
 

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I am not aware of any. There's not a lot of wiring behind the cab as the ABS sensors, speed sensor(?), lights, fuel pump, and backup camera and sensors are the only things back there.

I'm looking at wiring-in for a winch, I'm planning on running new cable from the battery.
Thank you
 

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Joel, I've found no evidence of a rear hot-at-all-times. I'm strongely considering adding a 100 amp in-line fuse up front and running a HaaT lead perhaps a #2 copper and splice that off for an Anderson plug to connect an inverter or any other items I want running while the truck is off or on, regardless, plus some bed lighting.
 

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Discussion Starter · #15 ·
Joel, I've found no evidence of a rear hot-at-all-times. I'm strongely considering adding a 100 amp in-line fuse up front and running a HaaT lead perhaps a #2 copper and splice that off for an Anderson plug to connect an inverter or any other items I want running while the truck is off or on, regardless, plus some bed lighting.
I'm leaning towards something like this too, but also including a second battery and a diode-based battery isolator. In my case I have some old 2/0 welding cable that I'll run front-to-back, put anderson 175A connectors at both ends of the truck, and be able to use the winch in both a front-receiver that I'm going to build and in the back receiver, plus be able to hook up jumper cables straight off of those anderson connectors, etc.
 

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TWX, thats a slick idea. I'm very leery of jumping cars w/ this beast, due to the horror stories of funky electrical gremlins in the Frontiers, but I was considering a dual-battery relocation as well. It'd get some weight off the nose and make space for the dual remote oil filter kit I'm planning on mounting, with dual PH8a filter elements. Only thing holding me back is like, well ya know, the $600.00+ of parts need to make this a reality, twin gel-cell batteries and all the other goodies. Que Sera, Sera. Maybe next year.
 

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Discussion Starter · #17 ·
I have the luxury of a lot of empty space under the bed with the crew cab longbed. If I do it I'm probably going to put the battery down there somewhere. I'm also thinking about onboard air though, and an air tank might be a better use for such a spot. We'll see what I end up doing and when.
 

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TWX, that was exactly what I was thinking as well. Haven't really got underneath with a flashlight n ruler but setting two AGM gel-cells sideways would prob fit up against the frame. Have to see what else might be in the way. My other option since I already have a toolbox that doesn't fit up tight against the cab wall, is to place a double-box or two single battery boxes in the bed between the toolbox and the cab. Would be a very protected space and wouldn't have to worry about water intrusion as I have a tonneau cover. Could also mount my compressor on the exterior of the toolbox, on the dead-space side.
 

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Discussion Starter · #19 ·
I've been also thinking about the space between the bed outer wall and the frame. It's not especially wide, but it may not need to be especially wide to hold a battery if the box for the battery is designed well and resists compression should the truck take a hit on the side of the bed. In my case this would be up in front of the rear axle.

If you see any good information on the actual installation process for a battery isolator circuit, I would love to hear about it. That's probably my biggest fear in doing this, I don't want to find that I've messed up the electrical system. Actually hanging a battery and stringing cable is not particularly hard by comparison.

I also wonder if a winch, either with or without a dual-battery setup, could use negative-ground to the truck frame instead of requiring cable all of the way back to the battery, even if it is necessary to increase the quality of the ground strap from the frame to the battery itself. Seems like it could save a bunch of weight that way, especially for really large cable.
 

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TWX, I wouldn't. You are going to be sending several hundred amps of current through the truck frame and with how twitchy the ECUs are in these Nissans, that sounds like it'd be a recipe for trouble. I'm going to run a power and ground all the way back to the battery, if I do drop a hot lead to the bed area. And if I move the batteries, I'm going to run a new ground all the way up to the engine bay and splice it in.
 
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