All wire has resistance.
Usually wire that is used to connect things together, whether its a car loom, a door bell or a supercomputer, is chosen so that its resistance is negligible relative to its function and if resistors are needed they are usually separate items. If the Bis ignition wiring is done with some non-standard resistive wire one would imagine that it would not just have the usual PVC sheath but in some way would be identified or clearly marked. Not putting it in the workshop manual makes it even more mysterious.
The only manual I have is the CD sold on this website, maybe there is other documentation available?
Ian