Tach hook up

[redfisher1]

1971 80 hp merc. 2 stroke. I'm missing wires on the switch box, but engin runs great. I would like to install a tach without useing the wire harness any suggestions would be greatly appreciated. I've included a picture of the switch box. Do I have to drill hole into engin casing to run a wire to the rectifier?

[Chris1956]

You should already have a brown wire in the harness. It was originally connected to the brown terminal on the switchbox, but if you want to use an aftermarket Tach, you need to connect it to one of the yellow wires on the rectifier.

If you want to run a seperate wire (no idea why), you can tape it to one of the control cables and run it into the motor on the port side. Then just route it to the rectifier.