[Healeys] Distributors - 67 BJ8

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Kees is quite right here, except for the resistance. It should be at least 1 Ohm when operating a 123.
We've made very good experience with 1.5 Ohms for 6 cylinder engines/high revving 4 cyl. engines and 3 Ohms for other 4 cyl. engines.
Eric
Brits 'n' Pieces (Germany)

...
The 123 ignition has the advantage of an adjustable advance curve. There 
are many options to choose from. As with most electronic ingnition check 
the coil (plus resistor or resitor wire) is 3 Ohms or more unless stated 
otherwise.
This system is very robust and rarely gives any trouble. if connected up 
properly.
Kees Oudesluijs
....