I got mine from the Norton Owners Club shop but with the wires for rear indicators (mandatory in Germany)
No major issue just snap them off.
It´s LUCAS 54956250 or WW19124.
I guess there is no other loom for that year and model.
Are you using the Rectifier/zener diode or a modern power unit ?
The cables for the zener are positioned for a 68-69 Fastback, which has the diode in front of the left hand side panel
and not in the right hand z-plate like the S-Type.