1990 convertible tach not working

[Dzire]

okay tach was working before I put in the new transmission so I put in the new transmission now the tach not working it does work for a second right when you start it up but then it stops any help on this is much appreciate

 

[Shadow102]

Check your grounds, the rpm I believe is read off of the cas and shouldn't have anything to do with the tranny.

 

[blackedoutFC3S]

I know this is super old, but the signal for the tach comes from the Trailing coil. Just disconnect both sensors off of there, reconnect them and turn the car on. Always fixed it on the ones I've worked on.

 

[Dzire]

put some new grounds on works great now