can someone tell me why my tach stop working and what could be the problem causing it?

 

the trialing ignition (igniter or pickup) could have failed. The tach gets its signal from them at the trailing coil. I would start with the ignition system

 

Have you noticed a loss in power, or a change in the sound of the engine?

It may be that the trailing igniter has failed. The tach gets it's signal from the trailing ignitor.

There are several threads with info on this. Do a search and you'll find plenty of info.

Welcome to the forum,
Brian

EDIT: Damn! 2GSLSE, you must have beaten me be just a few seconds.

 

1st thing to check for is a corroded tach send wire connection at the coil.

 

the tach wire likes to break