[rotorwrench]

The model A ignition system pretty well shows that Ford Motors was still on the low side of the technological ladder at the time. Their use of the breaker side of the circuit for the ignition switch was definitely different but when you compare the system to the Model T then it is still highly advanced by comparison. The other major gaff was putting the condenser in an area that can get pretty hot. Maybe that's why they made it so easy to replace.

There is an article in the Early Ford V8 Club's bimonthly magazine where a fellow experimented with condensers of values from 0.15 to 0.3 micro farads. The condensers were tested for resistance, leakage, and capacity prior to his testing so there would be some accuracy for results. All of them were automotive type capacitors of various part numbers and should have had a high end rating around 600-volts. His results were that he noticed no great difference in operation with any of them using the one can type coil for the test.

Pete is right about the resonance being the purpose. For each different design coil that Ford used over the years from 1928 through say 1956 for the 6-volt era, the condenser values were chosen by mathematical calculation to match the inductive reactance of each different coil design. For peak efficiency the resonance is important even though a small variation won't affect that efficiency all that much. It may affect the longevity of the points though.

Condensers can be placed on the outside of a distributor but it should be as close to the breaker points as is practicable. An original model A application has the breaker circuit that extends into the dash and then back out to the distributor through the armored cable so I don't know if I would call that a short run. If a person rewires it to put the ignition switch on the power in side of the coil then that might shorten the wire run from the coil to the distributor a bit. It just depends on whether a person wants to use the armored cable or not.

Back flow of energy released during the breaker opening can have a pretty high voltage. This information is pretty easy to find. Condensers need to be able to absorb that back flow during the magnetic field collapse. A capacitor doesn't care what the voltage is but the coil is affected by current draw depending on system voltage. This is why ballast resistors are used to control current in some applications.