We are trying to hook up a Nissan tach in my buddys boat which has a 140 Johnson,,his dad had this tach and it was pratically new,shame to waste it. On our Johnny motor it has,,black-ground,,,,,gray-which is tach lead,,,,,purple-which is switched power....he Nissan tach has green,yellow and white. The green is seperate and looks like a ground,,so I assume that it could be the yellow or white,any and all info much appreciated.