Momentary rocker switches are my favorite, this is usually what I install for customers but with a custom made steering wheel decal affixed.

https://www.digikey.com/en/products/detail/carling-technologies/V2D2GHNB-AAC00-000/483661

As the previous poster noted, wire the momentary switch between pins 1 and 4 of one of these.

https://www.digikey.com/en/products/detail/amphenol-sine-systems-corp/ATM04-4P-KIT01/4415005

Here is how to do your 585R to use the factory button on the hydro handle.

Find the handle DB25 serial port plug at the rear of the right hand console. Pull up the tray behind the switches and it’ll be obvious. Remove the connector housing. Remove or cut the wire to pin 17.

Connect that wire to one side of the coil (85 or 86) on a relay. Connect the other side of the coil to 12v.

Connect wires to 30 and 87 on the relay and wire to a Deutsch DTM/Amphenol ATM series female housing with male pins. Top two pins near the locking latch. Pins 1 and 4.

Plug said DTM/ATM into the remote engage plug on the OT3 ECU cable.

Call if you have questions, my contact info can be found through my profile.