Just sorting out a 1969 2+2. The tachometer works fine at low RPM,s. However it won’t go any higher than 2300 RPM. The car has a Petronix module instead of points.

any ideas where to start.

 

Most likely the Tach needs a rebuild. Common problem for that tach at this age. Nissonger does a fine job.

 

The Petronix shouldn't have any affect. Some cars have issues with the Tach when they fit a 123 tune dizzie. Could be the Tach or the feed to the tach

 

I guess nobody understands how this system works. The ignition system matters, and the tachnometer needs to be adjusted. On a '69, it's an easy task, because the tachometer can be adjusted without opening the case. There is a trimmer that can be accessed by an opening on the back of the case. It will covered by a rubber plug or if it's been adjusted before, by a piece of tape. Just pry it open and you will be able to reach the trimmer with an insulated screwdriver. Start the car and adjust to match any good shop tach.