Old Merc 850 Rev counter help

crazymac680 · 28 May 2010, 21:25

Hi folks
I've been wanting a rev counter for my engine but the last one I bought didn't work. I bought a Merc one and attached it to the Pos, Neg and Grey tacho wire and got nothing. Not sure why. Is there a third party tacho that would do the job?
Thanks for any help you can give.
Dan

Nos4r2 · 29 May 2010, 00:35

Quote:

Originally Posted by crazymac680

Hi folks
I've been wanting a rev counter for my engine but the last one I bought didn't work. I bought a Merc one and attached it to the Pos, Neg and Grey tacho wire and got nothing. Not sure why. Is there a third party tacho that would do the job?
Thanks for any help you can give.
Dan

If it's resettable, set it to 12 pole and attach it to pos, neg and a yellow wire from the alternator.As long as you're charging OK that'll tell you if the counter works.

9D280 · 31 May 2010, 11:16

Worth checking out the cabling too......

If it is gubbed, any "pulse counting" tacho will do the trick. I've got a Suz one that I've used on both the old Yam and the current Merc.

crazymac680 · 01 June 2010, 06:42

Thanks for the replys.
My counter doesn't appear to be working. 40 bucks down the drain.
Not to keen on forking out for another until I'm certain it's gonna work. Think I'll hold out for a pulse counting one going cheap on bay. I've gone 4 years without a tacho so I dont think my 1967 engine is in any immediate trouble.
Thanks
Dan

Poly · 01 June 2010, 07:33

Quote:

Originally Posted by crazymac680

My counter doesn't appear to be working.... 4 years without a tacho ...1967 engine

Are you sure its the tacho rather than the wiring from the engine.

In my limited experience I'd expect to see an a.c. voltage between the signal line and ground and this voltage will increase as the revs go up.

crazymac680 · 01 June 2010, 17:39

After reading about tachos on Iboats(http://forums.iboats.com/showthread.php?t=113463)
It seems I needed to make a couple of changes my rectifiers wires and may have broke my counter by using it before I made the changes.
Pretty sure the Tach is dead. It use to go to 0 when I put the pos and neg on but now it doesn't move.