Your wiring diagram (and the installation it relates to) is a home brewed job by the previous owner. Having two ignition coils was common on later 12V British BSA and Triumph twin cylinder bikes, but in the case they would not have a distributor as such, just a twin contact breaker plate, one set of points (Lucas 4CA or 6CA) for each coil cylinder, one coil for each cylinder. I believe the Series 1A interceptors were fitted with these in what most folks would still call the distributor body.
However, from your diagram it looks like P.O. has wired two 6V ignition coils in series to a single set of points, meaning both cylinders spark together, i.e. a wasted spark - not a problem with a 360° crank.
Most likely you've either got the Lucas 18D2 distributor with only the original points still operation, none of the original HT side of it now doing anything,
https://www.hitchcocksmotorcycles.com/p ... r_and_Horn
or you have got a pure contact breaker drive assembly retro-fiitted off another bike, e.g.
https://www.hitchcocksmotorcycles.com/p ... ng_harness
Does your present set-up actually work to your satisfaction? Would you want to change anything on it, apart from removing the surplus pair of ignition coils?
A.
