Tach for OB w/out alternator

[Paul Browne]

I'm trying to put a tach on my '79 50hp Johnson (which has no alternator),
and all I seem to be able to find are tachs that require an alternator
hookup. Does anyone know if it's possible to modify one of those to work for
me, or know of a tach (other than the TinyTach clipon, I want a dash mount
gauge) that will work? Any help/tips are greatly appreciated.

 

[IBNFSHN]

Outboard tachs connect to one of the leads from the stator. Usually a gray
lead.

 

[Paul Browne]

First of all, thanks very much for replying!

Yes, I saw in my wiring diagram that there is indeed a gray wire marked tach
lead...does that mean that I connect the wire that is supposed to go to the
alternator to that one? And I keep reading about alternator pole count...how
would I set that up?

 

[Jim]

Hopefuly one of the outboard mechanics will respond here. I suspect
that due to the age of that outboard and the fact that it's a Johnson,
you'll need a tach that you can set for 6 pulses per revolution. I
believe this cooresponds to a 12 pole alternator count. I have a '77
55hp that I needed a tach that I could set to the 6 pulses. My
brother's 100hp which is a bit older has the same setup.

-Jim

 

[Woodchuck]

Ask your question here www.screamandfly.com dedicated to mostly OB members

 

[Paul Browne]

Wow, thanks everyone for the great responses. I think I have my problem
solved now, thanks to all of you! Picking up a used tach at the boaters
exchange tomorrow, I'll let you all know how it goes. Thanks again!

 

[Paul Browne]

Well, between all the newsgroups/forums I've been reading, I've been able to
assemble a working system. Thanks to all of you for your help in getting me
setup, I greatly appreciate it. What I've been able to gather is that a CD
ignition system functions exactly like an alternator, so it supplies a tach
feed that is usable, (grey wire) even though it cannot charge a battery.
The only thing that isn't totally clear yet is whether I should use a 5 pole
setting or a 6 pole. I purchased a used tach this afternoon, and it works
beautifully off of the stator feed.

Thanks again everyone!