mercrusier Tach details

Ok, since I didnt get any response from my last inquiry about this darn thing, lets try it this way.
Mercusier outboard tach, 1977 500/50 new rectumfier.

The module mounted on the back, Ive seen it refered to as a resister. Does anyone know if thats what it is and if so whats the value supposed to be?? If not what is the purpose??
Still trying to find the cause of the low reading on my tach. It reads a good 2500 to 3 grand low.........or simply put, it wont over 2000 rpm.

Mercusier outboard? The module on the back I thought was for the older with points mercs.I am open to correction here.Try removing the module,then wire black > +,white > white on the lamp,and brown > neg .If there is only one wire on the lamp,put the white there and a jumper ground from one of the bracket points. I'm working on the assumption that mericrusiers work the same as outboards.You'll get advice from people who know in the mericrusier section.I have a tach which did not reach the rpm's that I felt that the motor was doing and I was told that it was for a six cyl motor and no pole for adjustment on the back,mine is a four cyl.

I was afraid that discription would be confusing. This tach sez mercurser across the top of the face, Im guessin its an outboard tach since it was in the boat with a 77 500/50 mounted, But you bring up an inyeresting point. No rul;e sez this has to be the correct tach for the application. HMMMMMMMMMMMMMMMMMM

Is that 500/50 3 or 4 cyl? Must be 4cyl. Is there a post on the back to change the pole? Do you know anyone with an older 6 cyl that will let you try it on their motor to see if it works?Or a mericrusier ?Or if a buddy could loan you his to try and see if you get a true reading,don't forget to put the brown to the rectifier yellow. The theory,if it works on either of those it's not the tach for your motor,And I'll know I wasn't been fed a load of male bovine excrement.

excuse me?????

Sorry, I meant the guy who told me that the tach I had was for a 6cyl wasn't feeding me the bull.... .I really must reread what I write to make sure I'm writing what I'm thinking.If that makes sense,and I was SOBER when I wrote that.

ha hahaha makes sense to me now!!!
As a matter of fact ive got the kind of tach your refering to on my 24fter Fiberform with a 165 mercursier and a spare in my shop. Ill be doin some testin and checkin in the next day or so.