Clutch was not engaging due to a bad connection. Fixed up the connector and the A/P works just like its supposed to. Thanks for the insight, Radomir.
Also, talked to my avionics guy today and he has some experience transferring the S-tec system from airplane to airplane. It can be done, but it can get expensive. There's the paperwork to buy, then all the airframe specific bits and pieces from the "installation kit"... And you guessed it, S-tec is the exclusive seller of those too.
Time to throw it on that "online auction place" (that rhymes with "fleabay") and see what happens.
WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.
Harmon Rocket II -SDS EFI
RV-8 - SDS CPI
1940 Taylorcraft BL-65