Ballast Wire System

Back to Minor Mods

Thanks to Tom O'Malley for the amazing Schematics from which to work.

Ballast Circuit & Solenoid Explained

And the simple installation of a Pertronix EI Unit

Specifically referencing my 1978 Federal Version Spitfire 1500, but I think there are many similarities to others. If you still have the Lucas Electronic Ignition (EI) system then the original schematic by Tom O’Malley (which is awesome) is how it should be wired, however, if a PO has changed it out, this wiring explanation may help.

Old Stuff

For those of us who no longer have the Lucas system, we can almost disregard everything to the right of the Distributor in the first schematic below except that at least on my car, the abandoned female 3-place connector (with 4 wires going in) remains under the Distributor coming out of the main harness, as does the Drive Resistor. The removed Lucas Distributor (held up here for illustration) still has the male connection with 3 wires going into the distributor housing.

Old Wire Routing

When I first looked at this I had a difficult time understanding just how they got 12 volts to the Distributor during start and fewer volts while motoring. It’s actually kind of opposite to what I thought and ridiculously clear now….

The Start Solenoid terminal (my “A” in the diagram) is fed by the solenoid only when the starter is engaged, which then pushes a full 12 Volts through the system along the un-resisted WY wire. When the starter is not engaged, that terminal is merely a connecter for the Ballast wire that reduces the 12 volts from the “On” circuit (terminal 3 of the Ignition Switch in this diagram) to 8.5 or whatever volts that the coil normally gets, then again along the WY wire. So simple when I don’t try to complicate things.

New Wire Routing

The instructions for my new coil states that it should not have an external ballast and it is not specific to EI or Points. So to avoid pulling apart my wiring harness when I put in the Flamethrower Coil and EI Distributor I merely took off the connector on the unimpeded, 12 volt side of the Drive Resistor and connected a wire from it to the +ve side of the coil. Then I had no need of the Ballast Wire or the other wire (WY) that originally went from the Start Solenoid to the coil +ve; I just disconnected both ends and taped them up (one day I’ll do a restoration and clean it all up). Of course the new Flamethrower Distributor has one red and one black wire that needed to be connected to the appropriate sides of the coil as well.

Sinfully Simple - The orange wire is the new one - this image shows just the new coil, distributor installation came next.

Starter Solenoid Operation

In the original configuration this is how the Starter Solenoid made its connections.

Not included here is the line to the Seatbelt Timer as it is self-explanatory.

Pertronix Review

I ran with the Pertronix EI and Flamethrower Coil for 3 years. Car seemed to start more easily and ran great.

I did read a few articles, apparently written by knowledgeable individuals who mentioned some of the drawbacks in aftermarket products such as finer bushings, so that’s another thing to consider when deciding if it’s something you want to do.

Hope this helps a few anyway.