Electric choke (+) / Pertronix ignition

[Bjv69ss]

Happy New Year!!!!!!!!!!!!
I was wondering if the coils (+) side would be ok to steal the power from for a feed for the electric choke.  I have a PERTRONIX set-up and no resistor.
Thanks!

[JohnZ]

Are you feeding the coil (+) with the original cloth-covered resistance wire from the bulkhead connector, or with a new non-resistance wire? Are you using a stock-type coil, or an aftermarket coil?

The Pertronix module red wire wants a full 12 volts for proper operation.

A stock-type coil wants a resistance-reduced 7-8 volts - 12 volts will eventually fry it.

The current Pertronix "Flamethrower" coil is designed to run on continuous 12 volts; most others aren't.

The electric choke also wants a full 12 volts, and draws current all the time; the wiper motor power feed (ignition-switched 12V) is a better feed source for the choke than drawing current from the coil (+).

[Bjv69ss]

John, I'm always learning from this site!

I did'nt realize the cloth covered wire was a resistance wire! 

I am using a Pertronix Flame Thrower coil with the ignition conversion.  What should I do.  Take the power from the wipers for both or can I cut the harness taping back and remove the resistor wire and feed both from there?

Thanks, Joe

[rich69rs]

John, I'm always learning from this site!

I did'nt realize the cloth covered wire was a resistance wire!

As JohnZ suggested, pick up the 12 volt source from somewhere else, wiper motor is one possibility, straight off of the battery is another.

There are two primary circuit wires from the ignition switch that connect to the + terminal of the coil; one wire for applying a full 12 volts for starting and a second "resistance" wire which reduces the voltage to the primary side of the coil when the engine is running.  The wires to the distributor and the tach lead (if you have a tach) connect to the negative (-) terminal of the coil.

When the ignition switch is in the start position, the ballast resistance (or resistance wire) is not in the circuit, and a full 12 volts is applied to the primary winding of the coil for starting.  After the engine starts and the ignition switch is in the "on"  or "run" position, the ballast resistance wire is now in the circuit and the other wire is not.  The ballast resistance drops the voltage from 12 to somewhere around 7-9 volts, enough for running while saving wear by reducing arcing across the points in the distributor.

Attached pic is typical.  It shows a ballast resistor in the "start" circuit.  Sometimes GM used a ballast resistor and in other applications GM used a special resistance wire of a given length to create the required resistance to drop the voltage from 12 to 9 or so.  Not sure of other years, but my '69 RS has the resistance wire which is easily identified by the cloth like material that covers the OD of the wire as described above.

On both my 66 Chevelle as well as my 69 RS, I have made the conversion to the Pertronix Ignitor electronic ignition with their flame thrower coil and all works just fine with the resistance (ballast) wire in place.  The Petronix electronic package is designed to operate between 8 and 16 volts.  The instructions clearly state:  "If your ignition system presently has a ballast resistor, do not remove it."  I would recommend that you do not modify the cloth covered resistance wire at all.  As mentioned above, when the engine is running you do not have a full 12 volts at the coil due to the resistance wire being in the circuit.  However, you should have enough voltage for the Pertronix package, especially if you have changed out from the stock coil to their "Flame Thrower" coil.  I have checked my 69 and I usually have 9 to 9.4 volts (Pertronix wants a minimum of at the + terminal of the coil with the engine running (resistance wire is in the circuit).

[68Zproject]

If you modify a switched 12 volt source to a dist, do you leave the resistance wire on the coil. or can you take it off and run the dist straight to the 12 volt source?

[rich69rs]

Straight 12 volts will eventually cause arcing and burn up the points.  Pertronix states that their system will work between 8-16 volts, but they also clearly state to not remove the resistance wire - if for no other reason to keep the electrical circuit "original" in the event someone would want to go back to a mechanical point distributor.  I would leave the resistance wire in place - which is what I did.  Output of the Flame Thrower coil with 9-9.5 volts on the +terminal works just fine for the way I drive my cars.  Racing applications may argue for more voltage at the +terminal.

[tom]

Interesting, I have the resistor, not the resistor wire. Is there a reason for one or the other, or any advantage or disadvantage?

Tom

[rich69rs]

Not sure why GM did it one way on some cars and the other way on others.  A buddy of mine used to have a '67 'Vette with 427 Tri-Power (never did understand why he sold that car 4 yrs ago) and the 'Vette had the ballast resistor instead of ballast wire.  One possible advantage would be the ease to change resistor vs. the resistance wire to fix a problem or tune the ignition system.

[Bjv69ss]

I guess I'll do what John suggested and steal the power from the wiper motor.  I don't have the dash harness back in the car yet so I'll need to check out the wire schematic for the right color wire to tap into. 

Thanks for the help!!!!!!

[JohnZ]

Pertronix has always done a poor job of explaining what they mean by "leave the resistor in place"; I've been through this countless times with Pertronix and with the Corvette guys, and what Pertronix really means is to leave the resistance in place (resistor or resistance wire) that feeds the coil (+) terminal if you're using a stock-type coil, as a full 12 volts will eventually fry a stock-type coil. The Pertronix module itself really wants a full 12 volts; the stepped-down resistance-reduced current from the coil (+) really puts the module on the ragged edge of functionality, especially at high rpm.

The diagram below shows how to connect a Pertronix with a stock coil (center diagram) or with their "Flamethrower" coil that runs on 12 volts (bottom diagram). The resistor shown is present on Corvettes - for a Camaro, it would be the cloth-covered resistance wire instead of a resistor.

[tom]

John,

Was the resistor sometimes used on Camaros? I ask because my 69 307 glide has one.

Tom

[Bjv69ss]

Thanks John!!!
That's much better to understand.  Now I understand!
Joe

[68Zproject]

That's  exactly what I was looking for.  You're the man again John Z, much thanks.

[JohnZ]

John,

Was the resistor sometimes used on Camaros? I ask because my 69 307 glide has one.

Tom

Nope. Camaros used the cloth-covered resistance wire. A previous owner must have added the resistor on your car. If the ignition switch side of your resistor is fed from the bulkhead connector by a cloth-covered wire, you're getting double-resistance in the circuit, with very low voltage to the coil.

[rich69rs]

From Pertronix tech support:

1.  The Ignitor does not need the resistor wire. It will work great on 12-volts. Overall a full 12-volts can be run to both the Ignitor module and the Flame-Thrower coil which has 1.5 ohms of internal resistance to work with the Ignitor.

2.  Coils from other manufacturers can be another story. Care must be used when using the Ignitor module with a non Pertronix coil.  If you are using a non Pertronix coil, in order to keep the ignition coil cool and to not "spike" and blow out the Ignitor you will need some resistance either prior to the coil (resistance wire or ballast resistor) or internally inside the coil.   

[RT Comment:  Point here being do not connect a switched 12V source directly to the coil if the coil does not have adequate internal resistance.  The safe approach is to leave the resistance wire or ballast resistor in the circuit to the +terminal of the coil.  (Refer back to the middle schematic in JohnZ's previous post.)]

3.  It is also correct to say that the Ignitor module would not "perform better" with more voltage. The higher voltage (12 volts vs. 9.5 volts) is only an insurance policy against low voltage which can occur as a result of a few issues. A poor battery or bad voltage regulators are a couple of them.

4  As far as the FlameThrower coil goes it is possible that full 12-volts could be beneficial from a performance standpoint.  Probably not felt in the "seat of your pants" though.