Major help with OEM tach and HEI
 

I have a 1970 K5 with a 350 and HEI, I installed a new bezel with a OEM factory tach. I connected everything by the book, but it still does not work when I run the engine. I read that a tach filter would work... Not. So, I installed a old 3rd party tach and it works great! I really want to have the factory look with the tach... Can anyone help me or point me in the right direction? Thanks a lot!