2000 dyna with side by side Speedometer and tachometer-Tach not working

[ΚĜΗΟŜΤ]

Friend has a 2000 dyna with HD speedometer and tachometer mounted on bars.

Tach stopped working.

My question is How does it work? Where does the signal come from?

Is there a magnetic type sensor/pickup that may need to be cleaned or something else?

Also is there an easy way to test if removed from bike?

Thanks
K

[rigidthumper]

Power (orange wire), ground (black), and signal (pink) are the three leads. If any of the three are missing, it wont read.
Power comes from the same place as the neutral lamp & oil pressure lamp, and shares the ground with the speedo. Signal comes from the ignition module. Check connections first, as that's usually the issue