I'll weigh in on this. I'm in the process of designing, building, and installing the electrical system for my new 912UL hung on the front of my Zenith 701 STOL, and I'm using the factory wiring diagram in the Rotax engine Installation manual as a general guide. I've had to educate myself as to aircraft electrical systems in general and this Ducati R/R in particular. Along the way I've learned the "factory wiring diagram" will work, but it has issues, and some are safety issues as far as I'm concerned. For example, if one were to wire the Ducati regulator as depicted in the manual, and wire the the battery directly to two items- the starter relay and battery master relay- as depicted in the installation manual, it certainty will allow you to start the engine. However, if one were to do so- and I wonder how many have- should either the start switch fail internally in the start position, or the start relay fail in the closed position at the moment one releases the start switch because the engine started as expected- the starter will continue to operate, and one would have no electrical means by which to shut down the engine. Not a good situation. So,after speaking to the Rotech technician regarding this issue (he was looking at the factory wiring diagram as we spoke over the phone and his response, and I'm paraphrasing here, was "hmm, I'll be darned") I'm deviating from the factory guide a bit. I'm wiring from battery only to the battery master relay, then from the battery master relay to the starter relay.This way I can interrupt power to the starter relay if need be by turning off the battery master. As a side note, I also asked the Rotech rep if there were any other Rotax sources for basic wiring diagrams for the Rotax 912 series engines other than their manuals. The answer is no, but he referred me to Bob Nuckolls' Aerolectric Connection. Also, after researching how an external regulator works, I've also come to the conclusion Mr. Miller's advice to separate the Control/Field wire from the regulator's output wires is sound and that's the way mine will be wired.
Just my $.02
Jim
