How do I rig up a tach to my 70hp Johnny OB?

[Challenger84]

I would like to install a tach on my OB but have no clue how.
On my controls there is a plug with three wires labels a,b,c. near the ignition key hole.
The controls say it's an OMC if that makes a difference.
Thanks in advance

 

[Challenger84]

Re: How do I rig up a tach to my 70hp Johnny OB?

If anyone needs a picture of it I can snap one if needed.

 

[Silvertip]

Re: How do I rig up a tach to my 70hp Johnny OB?

That's the plug for the tach harness. +12 volts, ground, and tach sense signal from the engine. You need to order the harness when you order the tach. Get it right here on iBoats.

http://www.iboats.com/Boat-Parts-Ac...*********.978132433--submit.x.24--submit.y.10

 

[Challenger84]

Re: How do I rig up a tach to my 70hp Johnny OB?

Thanks for the link but is there another way to connect the tach up without the harness?
Which one is the positive, negative , and sensor?
A=?
B=?
C=?

Thanks for the help

 

[Bob_VT]

Re: How do I rig up a tach to my 70hp Johnny OB?

A purple - hot
B gray tach lead
C black - ground

You really should get a manual with the proper diagram and use thew proper harness with a plug

 

[Silvertip]

Re: How do I rig up a tach to my 70hp Johnny OB?

I suggested the harness since you said you have no clue how to do this and if that's really the case you may not have the wiring skillls to use an alternate method. At the risk of doing other damage, here is another way. DO NOT DO THIS IF YOU ARE NOT SURE HOW:

1) Mount the tach in the console and set the calibration dial for your engine.
2) Find the grey tach sense line from the control box.
3) Connect that wire (splice into it if necessary) to the SENSE terminal on the tach.
4) Every gauge except the speedometer has +12 volts ("I" or "+"), ground, and light terminals. Connect the same terminals on the tach to the corresponsing terminals on any other gauge.
5) 16 gauge wire and ring terminals are acceptable.

 

[Challenger84]

Re: How do I rig up a tach to my 70hp Johnny OB?

When I said I had no clue was because I didn't know which wire goes to what.
I really appreciatethe help.
I'll have my tach up and ready soon .
Is there a tach that you would recommend for my type of motor?
I saw a ton of different tachs here on iBoats and would like to know the best one for my combination.
Thanks again!

 

[Silvertip]

Re: How do I rig up a tach to my 70hp Johnny OB?

They are generic but you need one for a two stroke.