Be sure to identify coil terminal by pos and neg, as marked, Robert
And read the last paragraph first - the rest is explanatory covering a set-up that has been tampered with by a PO, or the set-cannot be positively identified…
And are there any identification markings on the ballast unit, probably the ‘blue cylinder’?
Its a bit complicated; according to the wiring S2 diagram there are 3 wires connected to the distributor and 6 wires to and from the ballast unit.
Basically the ign system is very simple; a white wire from the ign key is connected to coil positive - and a black/white connects coil neg to the distributor. That’s all that is required for ignition.
However, refinements was gradually introduced - without necessarily updating the wiring diagrams to match each
car’s wiring in detail. Hence my apprehension…
To wit; an external resistor was added to protect the coil - which was bypassed while cranking, requiring wires. At the time; white/blue was powered in crank to bypass resistor. A further complication was routing tacho through the resistor unit the delivering ign power; with white/green to coil pos. In this configuration; the ballast resistor had white, white/blue green/? ‘in’. And ‘out’; white/green (to coil pos), white (dist), white/black (dist) - and a white/black from dist coil negative…
A different set-up connected the tacho directly to coil neg - simplifying the ballast resistor unit. Leaving the ballast with white and white/blue ‘in’ - and white/? ‘out’ from resistor to coil pos(!) - which looks more like your set-up? With a white/black from dist to coil neg…?
xj6 85 Sov Europe (UK/NZ)
To simplify; the purpose of a white/black, connected to coil neg from the dist, is to interrupt the coil’s ground connection to effect ignition. The white (powered with ign ‘on’) provides power to coil pos. The white/blue (powered in 'crank" only) is to bypass a resistor during cranking - to then increase coil voltage.