Re: tachometer
Try the grey wire for tach signal. Tach needs 12v on the purple wire (switched 12v per the ign sw.) and ground. If a Quicksilver tach, looking at the rear with it installed, the upper left terminal is purple or red with a purple stripe (BATT... switched via ignition switch), upper right is black (GND...battery -) and at the center bottom is the SENDER terminal for the gray wire.
Mark