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Old 05-24-2005, 11:09 AM   #1
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what operates on original 12volt?

We have a 74 overlander and we are wondering what is controlled with the 12 volt system? I realize thr ceiling lights, possibly the water pump. What about the exhaust fans, etc.? All seem to be original and functioning well when tested in trial. Is the converter a battery charger that keeps the batter charged up? thanks for any info.
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Old 05-24-2005, 11:14 AM   #2
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You pretty much hit is all. The converter does charge the batteries, though on some older units, it also cooked them.

The converter powers most of everything you pointed out, basically *nearly* anything that does not have an A/C plug touches the converter in some way shape or form when plugged into shore power.
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Old 05-24-2005, 05:05 PM   #3
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There is are 12v circuits that are kept separate from the converter contolled portion of the wiring harness, namely the running/brake/trun/backup lights and the electric brake activation wires which thke power from the TV. If there is a breakaway system it draws power from the house battery (implicated in the circuits you mentioned) and supplies it under certain circumstances to the brake magnets.

Also there is (usually) power to the "house" 12v circuits from the TV (and back to the TV battery) when the 7-way connector is hooked up.

Iam not disagreeing with your main point, and I'm not trying to be a smarty-pants but I do recall that when I first starting messing with the somewhat tampered-with wiring on my coach, woking out logically where power was flowing to and from helped me a great deal. Having the underway wires wrongly color coded gave me fits for a while until I got it that power should be there only when hooked to the TV.
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Old 05-24-2005, 07:39 PM   #4
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The main items that are NOT powered by the 12 volt house system are the air conditioning and the microwave oven. Most TV's are also not powered by 12 volts, but some can be.

Bob brings up a good point, often overlooked, that the 12 volt system for running lights, brake lights, electric brakes, and anything else that's chassis related is a separate 12 volt system.

The converter is a glorified battery charger with enough excess capacity to run your 12 volt items with a dead, or nearly dead, battery.

Your battery (or batteries) is the only connection between the house 12 volt system and the chassis 12 volt system. The battery will charge from the converter when you are plugged into 120 volt AC power. The battery will also charge from the tow vehicle (TV) whenever you are plugged into it. If you stay plugged into the TV and run enough 12 volt items on the trailer, you can deplete both the trailer battery and the TV battery.

The trailer battery must be installed and turned on, if you have a switch, whenever you are towing the trailer. It is the source of power for the emergency trailer brakes via the breakaway switch.

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Old 05-24-2005, 07:57 PM   #5
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Everything but the a/c runs on 12v. The original Univolt system does help charge the battery. Watch for overcharging though.

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Old 05-24-2005, 10:14 PM   #6
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Don't forget the "cigarette lighters". Back in the '70's they were used for powering cigarette lighters, electric shavers and television sets. Nowadays we call them "power points" and use them for powering cigarette lighters,electric shavers, tv sets, laptop computers, various handheld devices, and, my personal favorite, the XM satilite radio. And don't forget the old car stereo in the front end cap upgraded to modern standards, of course. My '73 has two of these power points, one in the bathroom and one in the living room next to the 'fridge. Enjoy!


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Old 05-25-2005, 02:26 AM   #7
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I can speak on my 70 overlander because I have a schematic and just covered the entire electrical system and dressed up the univolt cables. I also replaced the univolt since the series regulator was shorted and overcharging the battery. If you look at the 12 volts fuse panel, all 12 volt circuits are connected in parallel. Therefore the tow vehicle 12 volt will power all 12 volts circuits and the house battery will also power all 12 volt circuits. If anyone is interested in a free copy of the schematic I will be glad to e-mail it to you.If anyone has a schematic for the regulator board on the univerter or know the generic part # of the series regulator I would be interesting in it since I want to restore my univerter.
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Old 05-25-2005, 05:09 AM   #8
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wow! you were quick and very helpful!

Thanks for all the input. I now know what a TV is, and I DO have one! (don't have the other kind) I am looking into this for my husband and will pass it on, and see if he has any questions not covered here. I will also store this as mentally as I can for future use. All the research and reading I have done here and other places has come in handy over the 15 months since we acquired our first airstream. Once again, thanks!! You all are a wealth of knowledge and experience. We should be venturing out soon, at least for a weekend and apparently I will even learn how to manage all systems!!
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Old 05-25-2005, 07:52 AM   #9
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Frenchbern, I would appreciate the schematic of the electrical on your 70 overlander. It may help as well. We have the manuals for ours, but I'm not sure if it includes that. Thanks.
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