Kees - For the HALMET; if I lets say i want to ...
For the HALMET; if I lets say i want to connect my tank sender to the HALMET to A3 input. Do i then also need the A3 ground to the common ground of the engine? Or do I don't need to connect any grounds?
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And similar question for the digital inputs like let's say i want to have a D1 connected to my temperature alarm switch of motor that is also already connected to an alarm light.
My knee-jerk reaction always is that you should preferably have a ground connection close to the sensor to minimize the electrical "loop area". However, given that engines and engine panels seem to be often designed to just have one common ground for the dashboard, my knee-jerk reaction might not be realistic.
Having ground routed separately from the signal only results in noise induced in that signal. The AC inputs in HALMET nevertheless have fairly strong low-pass signaling, and I think it's unlikely that the noise would be strong enough to impact the digital signal inputs.
So, long story short, don't worry too much, as long as you have at least one ground wire to one of the Dx or Ax inputs. If you seem to have some spurious inputs, then try adding a ground wire close to the signal wire to reduce the noise.
OK thanks, What I just did is i connected all grounds together (D1 ground, D2 ground, A1 ground etc, etc,) and then have them all connected just to 1 wire that then goes to my engine ground.