tachometer confusion

[mr roach]

i have a 1977 merc. 115 i6 i picked up a couple of free tachs and want to install one my problem is one is a faria and it has the 4,6,8,setting and then it has a 12 pole setting with ( ob alt ) below it this is setting # 4 i think this stands for outboard with alt can i hook this up to my motor ? Part two my other tach has the 4,6,8 cyl and pulse settings plus a setting for 5p and 6p i take it this stands for pulse and i have a 12 pulse outboard and half of that is what i set the tach at and that would be the 6p setting would this be accurate ? Both tach only go to 6000rpm and i get conflicting info from faria's site and others as to whether i can use this on an outboard i am not a great at electrical but can do the simple to moderate type of work as always all replies are appreciated and thanks for helping out a newbie

 

[Silvertip]

Re: tachometer confusion

First Tach: 4-6-8 stands for 4-6-8 CYLINDER engine (as in I/O or auto type engine). The #4 setting is for a 12 POLE alternator which produces 6 PULSES per rev. So you set the tach to 12 POLE for your engine.

Second Tach: 4-6-8 are not PULSES. Again it stands for CYLINDERS on an I/O auto type engine. The 6P stands for 6 PULSE. You have a 12 POLE alternator which produces 6 PULSES so again, for your engine you use the 6P position.

 

[mr roach]

Re: tachometer confusion

thank you silvertip and the 6000 rpm will work ? some say i have to have a 7000 rpm tach for my engine

 

[Silvertip]

Re: tachometer confusion

thank you silvertip and the 6000 rpm will work ? some say i have to have a 7000 rpm tach for my engine

If your engine revs over 6000 rpm yes you need 7000. If it doesn't rev over 6000 no you don't.