Not sure of the details of the Autometer mechanical speedo, but I'll bet it's like all the others. Basically the cable drive comes into the speedo housing and through a mechanical gear drive drives the odometer. The speedo needle itself is driven by a magnetic coupling working against a very light hairspring return. The faster the drive plate (connected to the cable)turns the further the needle moves. There is not really a lot that can go bad on a new unit, but it does not take much resistance to prevent the needle from moving. So, if the gauges have been sitting around for a while, it may be "stuck" and need a little coaxing.
Another possibility especially if you're using the backwards cobra speedo is that it's being driven the wrong way and the needle is "pegged" on "0" and the odometer is working but counting down instead of up.
Tapped on the glass today after removing the cable one more time and reinstalling it. Wa-la,
it worked on the drive today. I have a feeling after sitting in the box for a year and a half, it needed just a little more "coaxing." Thanks for the help folks!
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