on my machine (2017 Wacker neuson sw-20) I have to activate the controls , push a hydro switch for 3 seconds, then it lights up and then set the flow control ( wide open for mower) on the right joy stick is operational and then pull the trigger to lock that flow to implement (mower) of course this is most likely different on your machine.Im not familiar with New Holland, but other brand machines have another button you push down after you engage the hydros to keep the hydro flowing constantly. I assume there are multiple buttons on the joysticks. Just use the process of elimination to find it. Good luck