How did the controls work for variable-pitch props?
Control by wire? As in electrically?  

Many of the small planes like Cessna Cardinal use an engine like Lycoming O-360 (4 cylinder) use a spring to return the blades to a flat pitch, and engine oil pressure to change the blade pitch. The control knob in the cockpit mechanically allows the oil pressure to change the pitch.  In other small planes, like a Bonanza, there is a set of counterweights instead of a spring to accomplish the same. No electric control at all.