Ignition Wiring

BBShark

Garage Monkey
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I am installing a 69 ignition/engine harness in my car. However, my car has a mini starter (without an "R" terminal on the solenoid). My car also has an early 90's style HEI with a separate coil (not in cap).

Been looking at 90's wiring diagrams and, it appears that there is no need for the wire that runs to the "R" terminal and then to the coil. The coil only requires switched power (in Run and Start) and the solenoid only needs the purple "S" wire (and Battery).

Is this right?
 

69427

The Artist formerly known as Turbo84
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Respectfully, the R terminal shunt wire to the coil isn't there to provide 12v to a 6v coil (You won't find 6v coils or 12v coils in any electrical engineering manual). That shunt wire is there to compensate for low battery voltage during cranking in winter conditions where the battery efficiency is low and the starter motor is drawing a lot of current trying to crank over an engine/oilpump filled with thick oil. The shunting of the ballast resistor allows the coil to charge up to the desired amperage/energy level despite the battery voltage being low during cranking.

HEIs and (computer controlled) EST distributors have dwell control circuitry in them to extend the dwell period during low battery voltage/cranking conditions to sufficiently charge the coil for startup.

IIRC, HEIs were spec'd/designed to work down to 6v.
 

vette427sbc

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Interesting! What would be the proper terminology for a coil designed to work with a ballast resistor, and one without?
 

69427

The Artist formerly known as Turbo84
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Interesting! What would be the proper terminology for a coil designed to work with a ballast resistor, and one without?

To be perfectly honest, I don't know. In the engineering world, we have all the necessary electrical specs for coils/inductors, and that tells us what the inductance is (the main ingredient for storing energy), and it will tell us other stuff like the dielectric strength (what maximum voltages the windings can tolerate), or peak current/wattage to keep from burning up the wires/windings (and a few other boring details).

But, in the automotive world, those specs aren't always available. You (and I) frequently have to just use some rules of thumb, experience, and common sense. No ignition coil is going to be ruined just by hooking it up to 12 volts, as this is nothing compared to the 150-300 volts that the primary windings experience/endure every time the points open and the plug fires. The main issue to always keep in mind is the current level/magnitude in the primary windings. If you have a points setup, a decent rule of thumb is to keep the peak current in the 4 amp range. This prevents the coil from turning into a toaster oven if you leave the ignition on when the points happen to be closed. If you have an electronic switching system/module (that doesn't require a ballast resistor), you can generally run the amperage up a touch (5-6 amps), as most decent ignition modules will minimize the necessary dwell time to charge the coil, keeping the coil power-dissipation/wattage from getting excessively high.

Cliff notes: If you're running a 6v points system in a vehicle, most coils will work fine without a ballast resistor. If you use these same coils in a 12v points system, it's best to run a ballast resistor to keep the primary current (and wattage) from going too high. Electronic ignition systems (that don't use ballast resistors) can run higher amperage in the coils because the duty cycle (and internal wattage) is generally lower.

(Well, this certainly ended up being a longer answer than I intended.)
 
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