Author Topic: Want to add accessory power wire for trailer  (Read 247 times)

Offline Henry

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Want to add accessory power wire for trailer
« on: March 28, 2019, 03:31:52 PM »
Hi:
Truck: 76 C-20 with 350, TH400, A/C, stock wiring except for addition of trailer electric brake controller and 6-way connector on rear bumper for trailer.

I am adding a breakaway switch battery to my trailer and so I need an accessory power wire(+12VDC) from the truck for it to charge. Where is the most appropriate place to get this power from? Would it be one of the terminals on the firewall junction block?

I am thinking of running a 12AWG wire with 30A in-line fuse from the firewall junction block to my trailer connector.

Regards,
Henry

Offline zieg85

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    • 73-87 GM squarebody extended cab and conversions up to 91 R/V series
Re: Want to add accessory power wire for trailer
« Reply #1 on: March 28, 2019, 04:23:34 PM »
I did that straight from my battery with a #8 stranded.  Used the same separate for a small winch on my old trailer
 
1985 C30 Custom Deluxe Ext. cab 5.7L TH400 3.21 
1985 C20 Scottsdale 7.4L 4 speed 3.21
1986 C10 under construction
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Offline 75gmck25

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  • 1975 GMC K25 Camper Special, 350/TH350/NP203
Re: Want to add accessory power wire for trailer
« Reply #2 on: April 17, 2019, 05:30:29 AM »
It appears that the original setup in my dual-battery '75 GMC was a trailer/camper power wire (not sure of the size) that ran directly from the aux battery to the camper. 

There was then a power relay mounted on the driver's side fenderwell so that the aux system only had power from the truck when the ignition was on.  You could use a similar setup to power the trailer off the junction on the firewall when your ignition was on.

My harness has a brown colored wire on the driver's side (comes out of the fuse box) that was used to activate the relay.

Bruce

Offline Henry

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Re: Want to add accessory power wire for trailer
« Reply #3 on: April 17, 2019, 10:25:09 AM »
Hi Guys:
Thanks for the advice. Considering my addition of this wire is simply to trickle charge the trailer emergency battery (which activates the electric brakes in case of breakaway), I think I am going to keep this new accessory wire at the firewall junction block for a couple of reasons: there will be a low power draw; my trailer connector accepts no bigger than 12AWG wire; and my OEM wiring diagram shows an optional 12AWG accessory power wire to be connected at the firewall junction block. My trailer is not attached to the truck 90% of the time so I am not concerned about a constant power draw. I plan on trickle charging the trailer battery from an external source when not attached to the truck.
Regards,
Henry