Ground wire from battery to the bed or tie into existing ground in 7-way plug?

flyinsquirel

New member
I'm planning out a power dist block in bed of a Tacoma. My cheap side is wanting to use the existing ground wire in the trailer plug so I don't have to use as much wire. Am I better off running 2 equal size wires off the battery or can I run just a positive and then tie into the trailer harness ground? I believe that wire is a 12-gauge, 10 at best.

For now this is to power my new Snomaster fridge and some led light strips and maybe a small 12v fan in the shell. In the future, who knows. I'd like to size big enough to run a B2B charger in the future. I was planning on using 8-gauge.
 

Alloy

Well-known member
My $0.0002....run 2 new wires with a fuse/breaker.........it will be costly if you connect into the existing system and something goes wrong.
 

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DaveInDenver

Expedition Leader
For your expected use an 8 AWG circuit is about the upper end for using the frame as the return. It's what I did personally in fact, 8 AWG run to a Sea Fuse 6 circuit block and 8 AWG tie to the frame at the block (it's got the ground bus) and the battery. I would not tap off the trailer wiring ground.

For a large current circuit I'd run a dedicated ground, talking 2 AWG or larger to a remote battery or a very large inverter or something like that. The problem with using the frame as your ground is keeping corrosion at bay. To get a nice, low resistance connection you really need to expose bare steel on the frame.

Getting some rust under the terminal when you're running a fridge or some lights isn't a big deal but if you're consuming real current it starts to matter. Say you're at 100 amps, with a clean, solid connection at 5 mΩ that drifts to a crusty, dirty one at 50 mΩ. This mean you get a voltage drop of 0.5 V that turns into 5 V.

It's not that it can't work, it's just that you have to take more care in workmanship and maintenance. Plus you have more crimps, more places for a connection to work loose.
 
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flyinsquirel

New member
That burned up engine looks awful. So 2- 8awg wires off the battery with a maxi fuse it is.

Is 8awg going to be big enough to run a B2B charger in the future or should step it up?
 

DaveInDenver

Expedition Leader
That burned up engine looks awful. So 2- 8awg wires off the battery with a maxi fuse it is.
Don't worry, think it through and practice good workmanship. Without knowing context you can't know the story about that photo. There have been plenty of fires throughout history in a completely factory wired vehicle.
Is 8awg going to be big enough to run a B2B charger in the future or should step it up?
Depends on how big your charger is and how long the run to it. For a modest DC-DC charger 8 AWG might be suitable. However if you're taking the time and considering future-proofing bumping up might save doing it twice. Even if a 20 amp charger would technically work on 8 AWG it won't work any poorer with 4 AWG. Of course it's also completely unnecessary to run a pair of 1/0 cables, so there's a realistic budget balance you have to consider.
 

shade

Well-known member
If you plan to run multiple circuits, this is the time to do a little work figuring out what you need now, and in the future.

I posted that photo from the article only to illustrate a potential downside, not an inevitablity. I hope you read the whole article. Adding additional circuits doesn't have to be complicated or expensive, and it's a good project most people can do right.
 

flyinsquirel

New member
Dave - yes, future proofing is what I'm attempting to do, just trying not to gold plate everything if it doesn't have a real benefit.

Thank everyone for the help. I'll run 2 wires to a fuse block and a ground busbar in the back with at least an 8awg, with a maxi fuse at the battery.
 

rayra

Expedition Leader
I chose to run a pair of 1/0 cables to the rear, for supporting a future receiver hitch mounted winch setup. And in the meantime I use it as a power bus for a whole bunch of other stuff, various 12v and 5v recharging ports, a 1000W inverter, connecting my rooftop / ground solar. If you are going to the trouble of routing a pair of lines anyway, why not plus them up to do more. The cost isn't that much more. And you are already doing the labor of routing and protecting the wiring.
Next thing I'm doing with it is putting a an anderson coupling near one end on a heavy 12' set of jumper cables, so I can also jump vehicles from the rear of my Sub.
 

shade

Well-known member
I chose to run a pair of 1/0 cables to the rear, for supporting a future receiver hitch mounted winch setup. And in the meantime I use it as a power bus for a whole bunch of other stuff, various 12v and 5v recharging ports, a 1000W inverter, connecting my rooftop / ground solar. If you are going to the trouble of routing a pair of lines anyway, why not plus them up to do more. The cost isn't that much more. And you are already doing the labor of routing and protecting the wiring.
Next thing I'm doing with it is putting a an anderson coupling near one end on a heavy 12' set of jumper cables, so I can also jump vehicles from the rear of my Sub.
I frequently run a winch on a car hauler trailer, so this is exactly what I'm considering.
 

rayra

Expedition Leader
Well there you go. Perfect reason to. Couple years ago I relocated the factory 7pin on my Sub from his departure-angle-ruining location on the hitch mount and put in the bumper skin next to the plate. The rotary cutoff in my rear cargo area power box was originally chosen as a way to cut power to a 1/0 extension likewise embedded in or right under the bumper. That way I can leave the exterior jack dead when not actively in use. I haven't added that extension yet, but intend to both front and back bumpers.
One of the business plans alluded to in the Pismo shutdown topic involves a 16' tandem axle enclosed cargo trailer / mobile workshop, which would also have rooftop film solar and a battery bank inverter setup. But I'd also jack it into the Sub in transit or when more power is needed.

I planned for four floor penetrations but have only done the main pair to date




You can see the 7pin left of the plate in this pic. There's room there to add an SB175 coupling with weather boot.

 
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