American Motors: 73amx tach, bench test, gauge cluster

Question
I replaced my gauge cluster with one from my 73 Jav parts car
and the tach would not work on either one.  I ran into the same problem when restoring my 69 Jav. This means I have four tachs that don't work?  Is there a way to bench test these tachs without expensive diagnostic tools?  

Answer
The 73 repair manual does not give any diagnostics for a tachometer. However, you should be able to test it by connecting it properly.
The tach has a (+) & (-) terminal.
The (+) runs to the terminal with the yellow wire at the solenoid.
The (-) terminal goes to the (+) side of the ignition coil.
If it doesn't work, disconnect the yellow wire at the solenoid and connect the (+) of the tech to the terminal by itself.
If it still doesn't work, your tach is probably shot.