I'd be happy to offer some input. Keep in mind I have not read this entire thread on this matter. The regulator is a good part. We have thousands and thousands of hours on them without failures.
First, the rotax manual clearly states that if the R-B regulator terminals are hot and C is open, permanent damage may result. I have ran into 2 failures do to 12v failure to the C terminal. I have contacted Vans and am awaiting for a reply from their engineering to track down the system failure as I am not able to track the exact path through their box via the online schematic. From what I have discovered is that avionics switch controls the 12v input to the regulator C terminal. IMO, this would be a bad thing do to. As it offers the pilot the opportunity to isolate this input resulting regulator damage. As a authorized Rotax repair center. And have done dozens of firewall forward 912ULS designs and installations. My solution until Vans engineering offers one. Is to take the regulator C terminal to the normally open side of the master relay for its 12V source. This offers a better solution then parallel R-B-C as per the Rotax manual, because this isolates the regulator from the battery when master is off. Which will result in a slow battery bleed from the diodes in the regulator. I have done this on 2 RV12's with 100% success. I hope this helps some. I will follow up when I hear back from Vans engineering.
Scott
First, the rotax manual clearly states that if the R-B regulator terminals are hot and C is open, permanent damage may result. I have ran into 2 failures do to 12v failure to the C terminal. I have contacted Vans and am awaiting for a reply from their engineering to track down the system failure as I am not able to track the exact path through their box via the online schematic. From what I have discovered is that avionics switch controls the 12v input to the regulator C terminal. IMO, this would be a bad thing do to. As it offers the pilot the opportunity to isolate this input resulting regulator damage. As a authorized Rotax repair center. And have done dozens of firewall forward 912ULS designs and installations. My solution until Vans engineering offers one. Is to take the regulator C terminal to the normally open side of the master relay for its 12V source. This offers a better solution then parallel R-B-C as per the Rotax manual, because this isolates the regulator from the battery when master is off. Which will result in a slow battery bleed from the diodes in the regulator. I have done this on 2 RV12's with 100% success. I hope this helps some. I will follow up when I hear back from Vans engineering.
Scott