Control a 12vdc power steering pump in a boat after I damaged original control circuit

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Joined Apr 23, 2019
I made an expensive mistake with re-fitting an electric over hydraulic power steering pump into my boat today: by starting with wrong polarity I seem to have cooked the circuitry which managed idling the motor when not under load.

The pump is branded by Hydrive but apparently sourced OEM from Mercedes. Anyhow, it still runs, but where it used to slow it revs when there was no oil demand (i.e. the helm hadn't been turned for about 15 seconds), it now runs full speed always - this doesn't mean it's always under load because when helm isn't moving the oil returns to the pump with out restriction apart from the piping - but it does mean the pump is always at full noise, using more power than necessary, and heating oil a bit (if not catastrophically.)

Question: is there a reliable sensor system that might allow me to switch the pump on when my hand touches the helm? Can the stainless steering wheel (connected to the cast helm valve assembly but otherwise electrically isolated from the aluminium boat) be rigged to sense touch like a touch lamp? Apologies if that's a ridiculous question.

I guess I could do a break-beam sensor shining on the back of the steering wheel if I fitted a disc of black - shiny - black - shiny to the spokes.

A rebuild of the original logic is also possible: run the motor at reduced revs until a significant current draw is detected, then apply full voltage until a few seconds after the load come off, but I'm primitive in circuitry, and also the pump was a noisy thing even at idle and if it can just come alive when I take the helm it might be easier to live with - I appreciate there will be a pause as it starts up which would have been horrible when it was fitted to a car, but in a boat I'm not steering lots of the time (have an autopilot working from different pump), this might work out with the right choice of sensor.

The fine blue wire in attached picture was connected to ignition so that pump started when key was turned on. After my reversing polarity mishap the pump starts as soon as power is available on main conductors. I assume I've killed the board in picture.

power steering w168.JPG