Trimble Remote Engage Foot Switch for EZ-Pilot. It will come with the correct connector installed to make it a simple plug and play connection (not shown in the image).
Same as Trimble part number 78150-00 ($265.08)
Once installed you must adjust the settings in the CFX-750 for it to work:
Settings -> Vehicle -> AutoSteer -> EZ-Pilot Setup -> External Switch -> Remote Engage
Trimble Remote Engage Foot Switch for EZ-Pilot
SKU: PFC-0014
C$99.99Price
Item is currently out of stock, but can be custom made for you.