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Old 02-26-2004, 12:27 PM   #1
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Hooking Up Trailer Battery to Tow Vehicle

Ok all you electrical advisors - I'm getting ready for the spring trips coming up and need to hook-up my trailer's battery to the tow vehicle. My trailer never had a 12v system in it when purchased new many moons ago. I've put in a system with a Group 27 battery as well as the Intelli-Power and Charge Wizard. My question is where to connect the charge wire from the umbilical. Does it go directly to the battery or should I connect it elsewhere? I would like to be able to run my fridge while driving and won't use the propane method for obvious safety reasons.

Thanks in advance for your advice.

FF
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Old 02-26-2004, 12:55 PM   #2
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12V wiring

Brad,

The original 12V wiring used a separate line from the tow vehicle to the trailer. Part of the reason was to allow polarity changes since back then cars came either positive or negative ground.

The separate 12V line plugged into a connector that was left of the tongue, near the starboard front corner.

The line went to a fuse and then to the battery terminal. The battery was mounted in an external box just under the front window.

I have the original wiring diagram. PM me a fax number and I will send it to you.

Sorry, this is only a partial answer, as the original set-up didn't have a charger or converter. I'm sure someone else will reply with instructions for installing a battery isolator or switch to keep your intellipower from backfeeding your vehicle battery.
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Old 02-26-2004, 12:59 PM   #3
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You have two different issues here.

The charge line should be at the plug from a factory equipped tow vehicle. I would run it through a 50 AMP automotive circuit breaker and attach it to the positive side of the trailer wiring bus. That is how Airstream does it now.

The refer, due to the draw should be on it's own wire with sufficient gauge to handle the current load. This same wire should be hooked to the tow vehicle so the refer can ONLY be powered when the engine is running and NOT powered from the trailer battery. The draw will kill the trailer battery in a short time period. This wire should be run under the vehicle and connected to a sufficient source for the amperage too. I would add a circuit breaker in the Engine compartment and also just inside the trailer for this wire too.
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Old 02-26-2004, 01:26 PM   #4
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Wire Size

The proper size wire to run a fridge and charge the battery is easy to determine.

Add up your most probable amperage draw, and use the 2% table here:


Appropriate Wire Gauge Size

Note that the 5% table is not recommended for 12 volt useage.
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Old 02-26-2004, 06:35 PM   #5
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Thanks guys. This helps alot. So will the wiring diagram. If not for this, then for other electrical concerns. My trailer originally did not have a battery so i will need to install a trailer wiring bus. Anyone have a picture of one of these busses so I can get an idea of what to look for and where to mount it?

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Old 02-26-2004, 07:05 PM   #6
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Wiring

Brad, there was a pretty good thread earlier this month.
Tow vehicle wiring
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Old 02-27-2004, 05:50 AM   #7
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brad

what are you towing with?

here is how i did my chevy http://www.airforums.com/forum...&threadid=3770

perhaps you could model your trailer buss after the distrubution panel in older univolts, but use modern fuses or circuit breakers instead.

i can dig up a pic if you like.

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Old 02-27-2004, 07:02 AM   #8
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John - I'm towing with a GMC Sierra extended cab 1500 with the 5.0. And yes, I would like to see a picture if you would be so kind as to dig it up. Thanks

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Old 02-27-2004, 05:16 PM   #9
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keep your 'gaard up!

hey brad

i cannot take any credit for this, here is a pic of a mid 70's univolt panel that was salvaged and mated to a modern power supply. my buddy rickstream came up with this for his '74 excella. works excellent.

gives you the best of both worlds, new supply and all of the gauges and indicator lights work. not an issue for you but still cool!

what you need to do is decide how many circuits you have, pumps, fans and lights etc. and go from there.

my trailer has two rows of circuit breakers and a copper bar feeding it all down the middle. all of the negitive wires are connected under one large screw terminal.

john
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Old 02-27-2004, 06:09 PM   #10
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Hey John - I don't mean to sound like a doofus, but this is for the 12v side of life, right?

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Old 02-27-2004, 06:24 PM   #11
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yes you are correct brad.

this is for the 12 volt system. if my trailer was in the back yard where it belongs i would quick snap ya a picture. my stock '92 system is very basic and laid out quite well.

however, it is about 100 miles away right now.

whatever you come up with, placing it as close to the battery and the supply line as possible is your best option. shorter leads will make things simple and less line loss.

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Old 02-27-2004, 11:50 PM   #12
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brad

check out bobhast's setup, you could make one like his....

http://www.airforums.com/forum...&threadid=9363

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