If your ignition is standard (apart from fitting the Lumenition) then you WILL have a ballast resistor wire in the circuit. The ballast resistor is inserted in series in the primary circuit between the ignition switch and the positive terminal of the ignition coil.
When the engine is running, its resistance provides a voltage drop in the primary circuit, which lowers the voltage applied to the coil. The coil is designed to operate at this lower voltage level and still provide the step-up transformer action needed, for secondary circuit operation.
However, during cranking, a parallel connection from the starting circuit by-passes the ballast resistor. The voltage available at the battery terminals at this time, will now be applied to the positive terminal of the ignition coil. This voltage will give a boost to the current flowing in the primary circuit. You will have a 6V coil so it will not provide 12V supply!
So, I don't think you can use the live side of the coil. I think mine is wired to an ignition live from the fuse box - that's a bit more work but you only have to do it once.
Tony
<font size="1">1981 2L FHC Cavalry Blue - very original & not rusty!
1980 3.5L V8 DHC Regency Red - on the road again.</font id="size1">