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Old 07-06-2008, 01:20 AM
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12v source from 24v system

I just bought (but don't yet have in my possession) a medium duty diesel box truck that I assume is a 24v system. I also assume there is a 12v circuit in it somehwere since there is a Ford factory stereo in the dash. I guess its possible they designed a 24v stereo, but I doubt it from an engineering standpoint. The truck in question is a 97 F700 with a cummins ISB, 24' box, and hydraulic brakes. GVW is either 23k or 26k, I forget.

But... I have to put a trailer brake controller in it for towing. If there isn't a 12v side on the fuse panel already, can I get 12v by connecting wires to the pos and neg of ONE battery, or will I find its all 24v once its hooked up in series? Will I just have to bite the bullet and install a converter? Do they make 24v brake controllers?

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Old 07-06-2008, 06:35 AM
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Have you measured the voltage? I think you will find that even though it has two batteries that its wired for 12 volts. The only trucks that I have seen with two batteries that were 24 volt systems have been military trucks.
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Old 07-06-2008, 09:20 AM
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re: 12v source from 24v system

It's a 12 volt system,the two batteries are for start duty's only.

Later
Kenny
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Old 07-06-2008, 04:39 PM
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Quote:
It's a 12 volt system,the two batteries are for start duty's only
I know that's true for light duty trucks, but as a commercial driver I know that big rigs, motorcoaches, and other larger (class 6 and up) vehicles are 24v. So I wasn't sure where this medium duty truck fell in.

Last edited by curtis73; 07-06-2008 at 04:45 PM.
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Old 07-06-2008, 09:48 PM
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I worked for a fleet of medium duty Fords in the 80s. Those were 8000 & 9000 series I believe??? Single axle, 9 ton ratings. Some were 475 & 477 Ford gas, some had 3208 Caterpillar v-8s. All had dual batts, and all were 12v.
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Old 07-07-2008, 04:31 AM
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Excellent. Good to know. I'll therefore assume that this one is 12v.

Thanks to all.
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Old 07-07-2008, 04:53 AM
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All of the big rigs and farm equipment that I have worked on ( and some had 3 batteries) were all wired for 12 volts. The only stuff that I have seen where its 24 volt is on military stuff.
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Old 07-07-2008, 06:40 AM
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Look at how the batteries are wired.....If they are joined pos-pos and neg-neg (parrellel), it's 12 volt. If they are wired pos-neg (series) and the other ends to the truck, then its 24 volt......

Also, if it is 24 volts, I would think there would be a big tag that says so.
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Old 07-07-2008, 01:43 PM
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I will look at it when I get it. I have to order things like a trailer brake controller, but I won't have the truck to look at until weds.

If it were here, I wouldn't have posted cause I could have checked in a heartbeat
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