What would cause my in dash tach to say 0 and my Auto-meter tach to read normal idle speed?

1. My in-dash tach revs witht the engine but is horribly inaccurate

2. Everything else on the dash works perfectly

3. The engine is running when i made these observations

4. 91 CRX HF with si motor and tranny and 90 pm6 ecu

It just started happening today so any advice would be great but the car as a whole seems to run normally

 

did u get your tach signal wire from behind the cluster. if so disconnect the wire for the autometer and run it to the blue wire on the dizzy plug its a 2 wire plug. i had the same problem thats how i fixed mine

 

mines hooked to the blue wire at the dizzy remember this is the in dash tach not working right and the auto meter works fine

 

If you have an autometer why are you worried about the tach in the dash?