Outboard tach doesnt work, auto tach does?? Why?

[ronsealdeath]

Hello,

Quick question; my 1977 Evinrude 55hp gives a reading with an auto tacho (RPM is not correct I know) but not with a Faria outboard I just bought. My rectifier is fryed and the charging system doesnt work. Is the faulty rectifier causing the outboard tacho not to register anything when the auto tach does? i.e. do they work in slightly different ways?

My Faria gauge could simply be broken but according to posts I have seen;

A faulty rectifier wouldn't damage the tachometer, the tachometer simply wouldn't work. This is due to the fact that the tachometer operates off of the charging system and the rectifier converts AC voltage to DC voltage, enabling the charging system. A faulty rectifier disables the charging system, and the tachometer simply doesn't register.

Why would the auto tach work when my rectifier is fryed? I assumed the tacho runs off a stator signal?

I'm confused!!!! Anyone got any ideas what may be going on?
Thanks
Al

 

[Will Bark]

Re: Outboard tach doesnt work, auto tach does?? Why?

It is my understanding that as you say; the outboard tach operates off the rectifier and if it is fried then you get no tach and no charging; doesn't affect the running of the engine. An auto tach operates off the firing of the #1 spark plug; completly different circuits.

 

[ronsealdeath]

Re: Outboard tach doesnt work, auto tach does?? Why?

THanks for replying, that sounds about right to fit the situation. I will replace the rectifier anyway as it needs doing, and see how I go
cheers
al