need info on old omc tachometer

[xjdriver]

Im hooking this up to my 1975 70hp evinrude, the tach sais 121707, im guessing the positive goes to the slotted screw? And ground to the nut in the center, but im not sure. It looks like it has 3 different settings, they're not marked so i dont know which to use.
Thanks, Rich

 

[seahorse5]

Re: need info on old omc tachometer

That looks like the old style OMC tach that only works on engines with ignition points. It will not work on your 70hp that uses the alternator for a tachometer pulse.

 

[xjdriver]

Re: need info on old omc tachometer

I looked up the model number, and i found one for sale which said it was an alternator tach, but i cant find any legit info on it.

 

[seahorse5]

Re: need info on old omc tachometer

You mentioned that there were 3 settings on the back, it's been a very long time but I don't remember them on the original alternator tachs, but I could be mistaken.

 

[xjdriver]

Re: need info on old omc tachometer

Well if you look at the pic of the back there is a metal jumper coming off the slotted screw and goes to one of three contacts. I also saw one similar which did not have a switched positive connection, just ground and pulse and it was an early alt tach.