Bill,

The older 200 series autopilots used the turn coordinator to control the turn rate.  It is a basic rate gyro.  It functions by introducing a signal opposite to the guidance signal.  Once the nomral rate of turn is reached, the guidance signal is nulled out by the rate gyro signal.  It's a bit more complex than that, but that's the nuts and bolts of it.

If the rate gyro is faulty, it may be saying "turn left" all the time.  Does the aircraft tend to turn the same way whenever the autopilot is engaged??

happy wiring,

Bob