1987 120HP Johnson - Need to add a Tach

[samm835]

I have a 24ft pontoon, my toon has always had Mercury or mariner motors installed. This year I had to replace my motor with a Johnson. I had to add an all new harness of course, but this didnt come with a tach. I know I dont have to have it, but I would like to know what my readings are. Can someone point me in the right direction on how to start this project? Can I use the old Mercury tach at all? Is it just a wires coming from motor to new tach? Thanks in advance for the help!

 

[JWhit]

Re: 1987 120HP Johnson - Need to add a Tach

Your control box should have a 3-pin connector at the bottom, below the key switch. That is the tach harness and you can buy the wire connection online and connect direct to the tach. don't see why the old tach won't work

if no connector the wires may be inside the control unit

 

[samm835]

Re: 1987 120HP Johnson - Need to add a Tach

Jwhit, Thanks for your help so quick! I was curious as to what that was, I can only imagine this harness isn't going to be a cheap thing! Again thanks for your help!

 

[JWhit]

Re: 1987 120HP Johnson - Need to add a Tach

Normally it's a small nub under the tension knob, which is under the ignition. I assume you have the normal OMC controls? The harness online is around $40, not a good deal but convenient. Otherwise you can splice in your own wires

 

[JWhit]

Re: 1987 120HP Johnson - Need to add a Tach

see this thread for wiring pics
http://forums.iboats.com/showthread.php?t=440296

 

[Sixmark]

Re: 1987 120HP Johnson - Need to add a Tach

Gray wire= tach signal lead

Purple Wire=12v pos lead

Black Wire= Ground