Tachometer Question

Hi Ya'll

On my Formula S, I have a tach on lower left dash. It is not working at this time. I don't find any tech stuff in the service manual. Wondering if it electrical, or mechanical. Any diag tips are appreciated here, been a while since working on an old Mopar
If it's a '65, it's electrical, but, needs a separate tach drive box that is usually mounted in the left kick panel toward the top.