A question about tach signal. Not where to wire it.

[knx2]

I have searched but cannot find an answer to my problem. I had an electrical problem in my car and everything works except the tach. I have switched out the cluster and have tried to wire an aftermarket tach to the wire in the ecu. yes I know which wire. Does anyone have any information on what the reading should be for the tach? For example the wire reads .34 volts on idle.