The feather button holding coil was activated by an oil pressure switch.
We did have occasional failures on DC3 and 4's and the procedure was just to pull it out manually.
The main point of misunderstanding runaways was the fact that the although the pitch lever was fully fine the propellor on DC3/4 started to fine off before full throttle and was constant speeding for take off and hi power.
In fact the max rpm for the engine is set by adjusting the CSU and not the engine.
On DC3/4 if the prop went into overspeed ( on the ones I was involved with it was metal contamination from CSU internal failures) the feather pump does not have sufficient pressure to overcome the CTM of a prop above its normal max RPM. Additonally in flight there is the effect of airflow.
Some of our pilot handing notes had a section on prop runaways and the procedure ( as noted by previous contributer) was the low and slow technique to reduce airspeed (airflow) and low to increase density altitude.
On some aircraft that had oil shut off cocks there was a final
pcedcure to shut of the engine oil cock to sieze the engine and have the porp shear off !! The notes said to fly in a circle so that the departing propellor went away from the aircraft
The propellor/ engine relationship is different between the big piston engines and the turbine engines.
In the days before CAA a typical ARB P & W 1830/2000 written question ( No multi guess
) was to draw the CSU and explain the controlling forces
