Tach not working

Thanks to the help here and my neighbor, my 710b is running perfectly and is a beast of a backhoe.

The last issues i am working out are all electrical. The tach is the one giving me a headache. It runs off the Alt which is charging at 14 volt at idle
The tach will jump when the key is turned on but show nothing while running. The wires are all good as are all the connections.
If I understand correctly the way the tach works is by reading the AC output from the Alt.

Any ideas?

Thanks

Tach not working