1150 Mercury 1978 Tach

[Tex51]

I have a 1978 1150 Mercury and I want to install a tach. I see the wiring harness on the shifter but this boat was unwired when I got it and have no idea which wires go to the tach. I barter for the boat and this is a project boat. I am going to have to put in all new gauges and wiring. The boat is a 16ft sidewinder clone. Thanks tex51

[Mercmx15]

You should have a black ground wire, white wire power from switch box and a brown wire from rectifier which will be your tachometer wire.
Think there 12 pole Tachs

[Tex51]

I have 4 wires in that wiring harness. 1- wire that is white with a purple stripe. 1 wire that is white and has a light bulb still connected to it from and old gauge I am guessing. 1 wire that is brown and 1 wire that is black. Now when I buy a tach does it make a difference if it is for an outboard or I/O or is there any difference? I am going to label the wires so next time I will know what they are. Thank you for helping me out. I have a large learning curve ahead of me.

[Mercmx15]

The colours I gave should be the colours at the motor end harness, you must have a adapter harness cable to a newer control box.
The motor end has a 7 pin and your will have 8 or 9 pin with different colours.
Google Mercury control wiring diagram and the different boxes will be shown, click google images

You are actually lucky you have a newer control box the one that came with that motor all had bad wiring where the wire coating would dry up and fall off the wiring. You just have to get the wiring diagrams so it all makes cense.
hopefully someone else chines in for you cause I have the older control box where the wires are the colours I said earlier.

SO YOU NEED A motor diagram and a control box diagram and no how to read them.
Good luck.

[Tex51]

Thanks for the info Mercmx15. I am going to look at the Mercury site and find the one I have. Thanks Tex51