On the x350’s, there is a yellow button to the left of the steering wheel. Hold button down then hit reverse pedal. Once you start backing up you can releases button and the blades will stay on til you release pedal.
On the x350 you have to pull up on the PTO switch that you use to engage the blades. It is called RIO or reverse implement option
There should be a button that you mash before you go in reverse with the blades on
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