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Old 07-09-2019, 02:51 PM   #1
Peter in NH
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Default Model B Coil Wiring

Should the wire coming from the ignition switch on a model B be attached to
the negative or positive side of the coil? Conversely should the wire going to the
distributor from the coil be attached to the positive or negative side of the coil?
I'm trying to figure out if I have my B ignition coil wired incorrectly as I have
a very poor spark at my distributor and don't know if my coil is defective or it's
due to incorrectly positioned wires.
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Old 07-09-2019, 03:09 PM   #2
Y-Blockhead
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Default Re: Model B Coil Wiring

If you have positive ground the positive side of the coil should go the ground (points).
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Old 07-09-2019, 06:10 PM   #3
Mulletwagon
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Default Re: Model B Coil Wiring

Not a simple question. Positive/negative ground, 6v/12v, ignition switch config, electronic ignition, was system ever modified. Wiring sometimes gets pretty creative over the years.
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Old 07-09-2019, 09:12 PM   #4
rotorwrench
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Default Re: Model B Coil Wiring

The old coils usually had "Dist & SW" abbreviations on the coil terminals during the positive ground era. Now days a person needs a coil polarity tester to make sure it's got the correct polarity.
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Old 07-10-2019, 05:34 AM   #5
Peter in NH
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Default Re: Model B Coil Wiring

My B has an original setup in that I'm running an original Ford script SX(Essex) coil on it.
Coming from my ignition I have the wire attached to the positive side of the coil (coil has
a plus and minus debossed on it). I have the wire to the distributer points attached to the
negative coil terminal. At the coil positive terminal my tester light is very bright. On the coil
negative terminal the tester light is barely bright enough to be detected. At the distributor connection point where the condenser and wire coming from the coil connect I have no
light. Do I have the coil wires incorrectly reversed or do I have a bad coil that is no
longer putting out correctly?
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Old 07-10-2019, 06:03 AM   #6
noboD
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Default Re: Model B Coil Wiring

Quote:
Originally Posted by Y-Blockhead View Post
If you have positive ground the positive side of the coil should go the ground (points).
what he said.
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Old 07-10-2019, 06:16 AM   #7
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Default Re: Model B Coil Wiring

However how you have it wired, it better go something like this: (Pos ground), hot wire to neg side of coil, pos side of coil up to the ign switch, then down to the dist. AMEN
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Old 07-10-2019, 07:41 AM   #8
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Default Re: Model B Coil Wiring

If you want to quickly and easily confirm proper coil polarity, you need one of these:

https://www.brattons.com/ignition-sp...il-tester.html

It's a nice item for a club to own in their tool kit, because you don't need to use it often. So you can share it around the club as needed.

When you are using a test light, as you describe, the points must be open or you must insert a little non-conductive piece of something between the points. A business card corner works well. If the points are closed, you get false readings.
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Old 07-10-2019, 09:07 AM   #9
rotorwrench
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Default Re: Model B Coil Wiring

Points closed equals a hot circuit with magnetism being generated in the coil core. It's going to drop voltage due to the electro-magnetic effect with resistance in the primary winding. The coil can get hot if it stays energized too long. If the points are open then there is no ground path due to the open circuit.

A coil has a single internal connection between the primary and the secondary coil windings. This connection has an effect on efficiency of the electro-magnetic effect. With a Positive ground system, the power is always on the negative side for battery and coil. The ground side of the coil is the positive terminal that is connected through the breaker points & condenser to ground. It is opposite of a Negative ground system. With so many different manufacturers of coils, its hard to say if the secondary connection is at the positive terminal or the negative terminal. This is where the coil polarity tester comes in handy but a graphite core pencil can also be used as a tester if you follow a procedure that will give a proper indication.

THis is a good link. https://mgaguru.com/mgtech/ignition/ig104.htm
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Old 07-10-2019, 01:53 PM   #10
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Default Re: Model B Coil Wiring

And just to confuse things more, on a generator system electricity always travels from ground to positive.
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Old 07-10-2019, 03:26 PM   #11
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Default Re: Model B Coil Wiring

Quote:
Originally Posted by noboD View Post
And just to confuse things more, on a generator system electricity always travels from ground to positive.
What if you have positive ground. Does the electricity travel from positive to positive??
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Old 07-10-2019, 05:29 PM   #12
rotorwrench
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Default Re: Model B Coil Wiring

Having a generator or an alternator doesn't make all that much difference. Even in a negative ground system the electron flow it still from negative to positive. This was why they used positive ground with the 6-volt DC systems. It gives a slight advantage when working with lower voltages like that. At 12-volts or higher, the advantage is pretty much nill.
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Old 07-10-2019, 06:16 PM   #13
Patrick L.
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Default Re: Model B Coil Wiring

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Last edited by Patrick L.; 07-11-2019 at 05:38 AM.
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Old 07-11-2019, 07:43 AM   #14
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Default Re: Model B Coil Wiring

Remember the peak & the pot-hole that develops in the point surface contacts! NEW points will fix that!
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