What you are looking for is the output named aux hydraulic relay (available both for cytron and ibt2)
See the steer. Png and other schematics in support folder. Same relay as what we use for 6/2 cut off valve.
or google: arduino 5v relay high level trigger
High level because it is 5V to activate (5V output from autosteer PCB)
If you have got a Kaupoi autosteer PCB ver4.1 then there is a SW out, which will be 12 V, only when automatic steering is on. (controlled by a Power fet BTS442E2 )
What you name “motors” are actually the right and left solenoids on a ordinary vickers proportional valve.