6 volt coil
Fleet Owner
Joined: Jul 2004
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From: NM
It's not a simple answer (although I like Vern's answer!)
Some 6v cars/trucks used a ballast resistor, so the coil was actually seeing less than 6v. Some used straight 6v. Most 12v coils run at an actual 7 - 9v because almost all use a ballast resistor, but some have the ballast inside the coil, so they get hooked up to 12v, while others use external ballast and connect to the reduced voltage.
What is your real question? What do you want to do?
Some 6v cars/trucks used a ballast resistor, so the coil was actually seeing less than 6v. Some used straight 6v. Most 12v coils run at an actual 7 - 9v because almost all use a ballast resistor, but some have the ballast inside the coil, so they get hooked up to 12v, while others use external ballast and connect to the reduced voltage.
What is your real question? What do you want to do?
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From: Buckeye, AZ
What I had thought before was that a 6 volt coil had less, heavier gadge windings than a 12 volt coil as is with most all things found in a 6 volt system.
This morn I did an ohms test on both as were known good.
6 volt: neg term to secondary post = 4.76 k ohms, pos term to secondary post = 4.76 k ohms, 1.5 ohms from positive to negative terminals.
12 volt: same as above tests with 9.69 k ohms either side and also 1.5 ohms from + to -
12 volt from what I got had twice the resistance as the 6 volt coil.
I know from personal exsperiance that the coil from one voltage will not work in another for very long without burning out.
This morn I did an ohms test on both as were known good.
6 volt: neg term to secondary post = 4.76 k ohms, pos term to secondary post = 4.76 k ohms, 1.5 ohms from positive to negative terminals.
12 volt: same as above tests with 9.69 k ohms either side and also 1.5 ohms from + to -
12 volt from what I got had twice the resistance as the 6 volt coil.
I know from personal exsperiance that the coil from one voltage will not work in another for very long without burning out.
Posting Guru
Joined: Jun 2008
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From: Buckeye, AZ
In repost and a little more thought both coils have 1.5 ohms on the primary side (+ to -)
but the 12 volt coil has twice the resistance at 9.69 k ohms than the 6 volt coil at 4.76 k ohms on the secondary side from negative to center post.
I'll bet there is an exception but I have never seen a 12 volt point ignition system that did not have a external ballast resister either in the form of a special 6 foot wire taped into the harness or a external block
mounted to the fire wall and without one on a 12 volt system would burn up the points in short order.
On same note at least on stuff Ive been around (stock) 6 volt systems never had a resister in line from the switch to coil pos. post.
but the 12 volt coil has twice the resistance at 9.69 k ohms than the 6 volt coil at 4.76 k ohms on the secondary side from negative to center post.
I'll bet there is an exception but I have never seen a 12 volt point ignition system that did not have a external ballast resister either in the form of a special 6 foot wire taped into the harness or a external block
mounted to the fire wall and without one on a 12 volt system would burn up the points in short order.
On same note at least on stuff Ive been around (stock) 6 volt systems never had a resister in line from the switch to coil pos. post.
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Junior User
Joined: Feb 2008
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what i was trying to say earlier is i am trying to crank my 52 ford v8 with out spending a lot of money on the six volt system because i was going to upgrade to twelve volts during restoration. any suggestions would be helpful. i have power going into the coil, but none coming out.
Elder User
Joined: Oct 2003
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From: Canada
Just for the record, I ran a 12 Volt coil on my 51 Merc for over 6 months before I had known it was in fact that.
My 51 was a 6 volt system, and the only reason that I found out was when I did the adjustment on the valve lifters, as I had one or 2 ticking.
Put on a 6 volt coil and and there was no difference at all, and I never burnt out any points.
Prior to the 51 Merc, i had a 50 Ford and ran it on an 8 volt that is when the trouble began. Never ever will I run an 8 volt battery, nothing but a pain in tha a??.
Where a lot of guys go wrong on the 6 volt system is they run the 12 volt battery cables and they won't do the job.
Make sure your starter is in proper working order, and your cables are heavy enough. I make up my own with o/o guage welding cable and soldered terminals, and good clean contacts.
Hell these old buckets started in sub zero weather back in their day, so why shouldn't they start now.
I get my batteries from TSC, the one I run is 940 CCA.
If that won't start your flathead then you have another problem.
Another item I found that works great and that is the Petronix ignition and its available in 6 volt.
My 51 was a 6 volt system, and the only reason that I found out was when I did the adjustment on the valve lifters, as I had one or 2 ticking.
Put on a 6 volt coil and and there was no difference at all, and I never burnt out any points.
Prior to the 51 Merc, i had a 50 Ford and ran it on an 8 volt that is when the trouble began. Never ever will I run an 8 volt battery, nothing but a pain in tha a??.
Where a lot of guys go wrong on the 6 volt system is they run the 12 volt battery cables and they won't do the job.
Make sure your starter is in proper working order, and your cables are heavy enough. I make up my own with o/o guage welding cable and soldered terminals, and good clean contacts.
Hell these old buckets started in sub zero weather back in their day, so why shouldn't they start now.
I get my batteries from TSC, the one I run is 940 CCA.
If that won't start your flathead then you have another problem.
Another item I found that works great and that is the Petronix ignition and its available in 6 volt.
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Fleet Owner
Joined: Jul 2004
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From: NM
In repost and a little more thought both coils have 1.5 ohms on the primary side (+ to -)
but the 12 volt coil has twice the resistance at 9.69 k ohms than the 6 volt coil at 4.76 k ohms on the secondary side from negative to center post.
I'll bet there is an exception but I have never seen a 12 volt point ignition system that did not have a external ballast resister either in the form of a special 6 foot wire taped into the harness or a external block
mounted to the fire wall and without one on a 12 volt system would burn up the points in short order.
On same note at least on stuff Ive been around (stock) 6 volt systems never had a resister in line from the switch to coil pos. post.
but the 12 volt coil has twice the resistance at 9.69 k ohms than the 6 volt coil at 4.76 k ohms on the secondary side from negative to center post.
I'll bet there is an exception but I have never seen a 12 volt point ignition system that did not have a external ballast resister either in the form of a special 6 foot wire taped into the harness or a external block
mounted to the fire wall and without one on a 12 volt system would burn up the points in short order.
On same note at least on stuff Ive been around (stock) 6 volt systems never had a resister in line from the switch to coil pos. post.
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From: Buckeye, AZ
The only thing I can figure out without any thing to back it is the primary windings on the 12 volt coil with external resister and the 6 volt coil were only 1.5 ohms which is why I didn't get any real different reading from either side to center as we are talking in thousands of ohms on either coil secondary. I can get a six volt coil but is not called for positive or negative ground systems or I wasn't paying attention at any rate a few times I have used the lead end of a lead pencil held between the coil wire and the block to be sure of the polarity of the hook up, noticed some coils lacked markings for hook ups.
I find my self in need of correction as I stated earlier I never saw a 12 volt system that did not have an external resister but beside the two I listed there was one that was a Autolite coil with a resister incorperated within the coil housing but was used on 53-55 Chysler Imperials also last but not least a coil with higher primary resistance only, I wonder if these were the times when working on 12 volt ag equipment, gas powered that I cursed the last idiot that worked on it for throwing away the ballast resister when by the time I got to it with a new coil already installed was burning up points regular?
Had this happen recently in a New Holland.
I find my self in need of correction as I stated earlier I never saw a 12 volt system that did not have an external resister but beside the two I listed there was one that was a Autolite coil with a resister incorperated within the coil housing but was used on 53-55 Chysler Imperials also last but not least a coil with higher primary resistance only, I wonder if these were the times when working on 12 volt ag equipment, gas powered that I cursed the last idiot that worked on it for throwing away the ballast resister when by the time I got to it with a new coil already installed was burning up points regular?
Had this happen recently in a New Holland.
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