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Old 03-01-2015, 11:59 AM   #1
Pfdchief
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6 or 12?

My 55.2 gmc was not running when I got it. I thought I read that in 55 GM switched to 12 volt system, but looking at my heater motor it say 6 volt on it. Can anyone shed any light on this for me??
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Old 03-01-2015, 02:14 PM   #2
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Re: 6 or 12?

Pretty sure the 55.2 was 12 volts. The 6v heater...maybe someone replaced it with what they had? And will defer to an expert.

Will you be rewiring the truck Chief?
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Old 03-01-2015, 02:57 PM   #3
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Re: 6 or 12?

Here is a suggestion for stovebolt.com tech sheet on converting to 12v. It will allow you to use the 6v heater assy.

"Put a voltage reducer* in the power line to each 6-volt accessory switch (radio, heater, etc)"

"Check with your parts dealer for the correct part numbers for these items. I went back and checked my records and I actually bought my voltage reducers from Jim Carter's Antique Truck Parts, 1508 East Alton, Independence MO (816) 833-1913. Specifically, they were:
Part# EL110 Voltage reducer (Light duty for gas gauge)
Part# EL135 Voltage reducer (Heavy duty for accessories)
Part# EL181 Voltage reducer (for ignition points)
The part numbers may have changed since 1995 when I bought mine"

Or you can start looking for an original 12 v unit, sort of readily available in the south where guys convert to modern heat A/C units. There is currently one on the Boise Craigslist autoparts page but don't know if the guy will ship (not mine).
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Old 03-02-2015, 11:52 PM   #4
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Re: 6 or 12?

Just to be sure this is a 55.2 GMC

I know, I know I just want to sure we're on the same page ....
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Old 03-03-2015, 09:57 AM   #5
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Re: 6 or 12?

Yes Sir. 55.2
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Old 03-03-2015, 12:42 PM   #6
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Re: 6 or 12?

55 second series were 12v, some one may have changed the heater or blower motor from an earlier truck.


You can look at the generator, 12v generators have a red tag and 6v tags are black.
coil should also be marked 6v or 12v.
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Old 03-03-2015, 02:38 PM   #7
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Re: 6 or 12?

55 GMC Second Series is 6 volt Positve Ground. In 56 they switched to 12 Volt

55 Chevy Second is 12 Volt negative ground.

However do some checking to be sure someone over the years has not updated it to a 12V system. A lot can happen in 60 years.

Last edited by paulspickupparts; 03-03-2015 at 03:01 PM. Reason: e
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Old 04-15-2015, 04:26 PM   #8
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Re: 6 or 12?

Silly question. How do I know if it's 6 or twelve by looking at it?
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Old 04-15-2015, 05:32 PM   #9
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Re: 6 or 12?

Quote:
Originally Posted by paulspickupparts View Post
55 GMC Second Series is 6 volt Positve Ground. In 56 they switched to 12 Volt

55 Chevy Second is 12 Volt negative ground.

However do some checking to be sure someone over the years has not updated it to a 12V system. A lot can happen in 60 years.
the longer i'm here, the more i learn
i would have stuck my size 14 in my mouth by stating a 55.2 gmc was a 12 volt system
like the chevys
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Old 04-15-2015, 05:54 PM   #10
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Re: 6 or 12?

sorry Ogre. I meant without a battery. The reason I ask is my truck is a 55.2 gmc but the previous owner said it was 12 volt. So I put a 12 volt in it neg to ground and it turns over, just not really fast. Not even sure which way it was turning over. f it's hooked up backwards would it even still turn over?
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Old 04-15-2015, 05:57 PM   #11
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Re: 6 or 12?

Just found in another thread to check the lights. Thanks.
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Old 04-15-2015, 09:19 PM   #12
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Re: 6 or 12?

Quote:
Originally Posted by _Ogre View Post
the longer i'm here, the more i learn
i would have stuck my size 14 in my mouth by stating a 55.2 gmc was a 12 volt system
like the chevys
Me too and I did...I am always learning from this forum.
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Old 04-15-2015, 05:28 PM   #13
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Re: 6 or 12?

each cell in a lead acid battery puts out 2 volt
6 volt battery typically has 3 fill caps, 12 volt will have 6 or none


6 volt



12 volt, each cap covers 3 cells

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Old 04-15-2015, 06:28 PM   #14
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Re: 6 or 12?

Look at the generator and light bulbs. The starter will spin correctly hooked up either way.
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Old 04-15-2015, 09:50 PM   #15
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Re: 6 or 12?

I looked at the generator. All that's on it is one part number. I pulled the rear rear tail light and it was a 1124 which is a 6volt I believe. Thanks guys.
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