General Can you Replace old Speedo with new type

[amdtony]

I have a 2000 jtd 105 ELX multi with the older instrument panel. It has the speedo and fuel guage but no RPM.

My question is can you fit one with the RPM on it or would it be pointless as there would be no wire to control it (make it work)?

Any thoughts would be appreciated.

Its my first post so go easy on me.