From the flight manual.
PROPELLER FEATHERING SWITCHES. Each propeller is feathered individually by one of the four red push button switches above the central control panel on the instrument panel. Pushing the switch in starts an electric pump in the nacelle which supplies hydraulic power for the feathering operation. When the propeller is fully feathered the push button automatically releases, stopping the pump. To stop the operation before feathering is complete, pull out the switch button by hand. To unfeather a propeller, the push-buttons witch must be manually held in the closed position until unfeathering has been accomplished.