so i restored my dads boat replaced all wiring, did a continuity from brown wire on the switch box up to tach side of my merconrol, it checked out fine same with ground wire back to engine cowl, original instructions with the gauge say green to green on tach wiring harness, but i get negative deflection, same when wiring directly to switch box, but get a positive reading when wires are reversed black to green and green to black what am i missing, help!
