I have a 1985 150hp serial# 6617084 on a boat I just purchased. It doesn't have a tach in it and I would like to put one in. Does anyone know which wire I need to hook to? I hope it's already through the connector and up to control box. If not I can run one easy enough. What type of tach do I need to buy for this motor? This is my first outboard and am worried about over revving. What would be a safe red line? Any help would be much appreciated.