I have a 1995 A6 Quattro with a 2.8. Two different problems appeared more or less simultaneously. The HVAC quit working, totally dead, wont turn on. The transmission makes a horrible screeching when shifted into park or neutral, it is OK when you start it, but once you shift into another gear and then shift back to P or N it screeches. I looked up wiring diagrams for the HVAC and trans control systems and don't see any common grounds. What am I missing here?