Beta rev counter failure

[Habebty]

Can anyone point me in the direction of likely causes of a rev counter failure?

The rev counter is 8 years old and I have recently a new alternator fitted.

The rev counter needle briefly twitches when the engine is stopped and started.

From the Beta wiring diagram, it looks like the rev counter is fed from a wire from the alternator. Can I use a simple multimeter to check if the correct voltage is being fed to the instrument? Or does it rely on pulses from the alternator?

Any other things to check with the instrument itself?

Thanks

 

[earlybird]

The W terminal on the alternator should show ~8 volts AC to ground, note not DC.

 

[Billjratt]

If it failed when you fitted the new alternator, the problem seems to be self-evident.
Tacho pulses are the raw AC from the alternator winding - an extra terminal (W?) it will measure 12 - 15Vac in relation to negative. If your new alt doesn't have the correct connection it is dead easy to add.
I assume the kick of the tacho at startup is just the ign power being applied rather than a kick when the engine trurns.

 

[santavey]

Same thing happened on my volvo.
Transpires that if the rev counter is not working the alternator isnt charging either.
Fault traced to a broken exciter wire.
Exciter wire runs from the starter to a terminal on the alternator. Cant remember which terminal.

 

[nigelmercier]

They are fed with an AC voltage from the alternator, about 12V peak to peak; you will probably get a reading of about 3/4 of this with a meter on AC volts.

Are the batteries charging OK?

 

[Habebty]

They are fed with an AC voltage from the alternator, about 12V peak to peak; you will probably get a reading of about 3/4 of this with a meter on AC volts.

Are the batteries charging OK?

Yes, the batteries appear to be charging ok. At least I can start checking the wiring now I know how many volts to look for.