You want to expand your existing printer on another extruder? In the current solution plate RAMPS1.4 outputs for all fans does. The solution is to extend the RRD FAN Extender. Which you get 2 additional outputs for additional fans.
2 controllable channels (D6 and D11)
max 0.5A per channel
Simple connection, simply plug in the board RAMPS1.4 and start using it.
Support firmware Marlin - "#define motherboard 34"
Wikipedia link here.
Inspiration for involvement in English here.