(DG) ACU-300 Ground - why is it important?

Hi,

I'm in the process of installing an ACU-300 (for solenoids) with rudder sensor, P70Rs and Tiller.

I have a hard time finding a decent connection for the ground pin. The documentation states, it should be connected to ship's ground (which is the steel hull, to which I don't have access at the location where the ACU is mounted) or directly to batterie's minus pole with a thick cable (wich is very complicated because the batteries are located somewhere else and there is no space to route a thick cable).

At the moment I've connected ground to minus of the ACU's power terminal. So ground is connected to batterie's minus (2,5qmm2 cable in 24V system), but not with a dedicated, direct cable.

Q1: Can you explain what's the reason the ACU has a ground pin in the first place?

Q2: What consequence could occur when Ground is simply connected to minus of ACU's power terminal?

Thanks!