Re: Tach for a 1975 Johnson 70 hp outboard??
Likely the factory left a grey wire stubbed out inside the control box. You can open up the box and extend the grey wire through a small hole drilled between the two halves of the box-on the bottom. This is the signal wire for the tach. All you need is + and - from the dash (-and maybe a wire to run the light inside the tach) and you'll be in business. You will have to set the marine tach according to the instructions-usually the switch on the back needs to be set to 6.
