How to test tachometer

The tachometer of our Midget doesn't move it's needle.
Is there a way to test the tachometer, so we can check if the tachometer is
defect or
that something is wrong in the wire-ing?

It's about an Midget MKII, positive earth.

Thanks,
Jan Bos

Midget MKII 1964
http://mg.janbos.com

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