A question about how to connect the pump to the Spark without the control board. Is it correct to connect the blue wire to the + digital output for actuators? The black and brown wire to the MDR-100-24. What to do with the - digital output for actuators?
Connect the minus of the Spark output to the minus of the pump, at the pump. You should have 2 wires next to each other going from spark to pump.
Voltage is relative, so for the control signal of 5V to be equal at the spark and pump, they need to have the same reference at both locations, by connecting both the signal line and the reference (GND/minus). The signal is “5V higher than GND”, so you need to connect GND, otherwise you get what they call a ‘floating signal’.