I am not that familiar with the ST3000, years ago I had a ST4000.
It appears the ST3000 has a compass
built into the control head
. The ST4000 uses a separate fluxgate compass
. So at a minimum you will need purchase
the compass in addition to the ST4000 control head.
The specs on the two units show the power consumption
to be the same, so it is likely the ST4000 control head can drive the ST3000 motor
. You might talk to Raymarine
to get their opinion on the motor compatibility, but it appears the only thing you will be saving is an old drive motor. Maybe best to replace the whole thing.