changing the gauges on my 2001 merc optimax to std gauges, there is a gray wire coming off ECM shows as tach lead, is the just a plug in there or do you need to unhook smartcraft harness or ?? also the trim sender is a 3 wire deal now and digital I'm told, need to covert to a std analog sender I think..Anybody ever done anything like this ? thanks Rob

Mercury makes a digital to analog converter box. This is the way to do it!

that only works on 2002 and and later, 2001 is a bastard year, been a year messing with smartcraft gauges