Try this link to the HAMB. If you join, read the rules first. But you’ll probably find what you need somewhere here.

https://www.jalopyjournal.com/forum/search/125964263/?q=Sun+tach&o=relevance&c%5Bnode%5D=5

miker
55 bird, 32 cabrio F code
Kent, WA
Tucson, AZ

This is the tach

Sounds like the old Sun tachs that had a separate sending unit that was usually installed somewhere under the hood.  The sender had batteries in it, and the pulses from the ignition determined how much of the battery voltage was sent to the tach, which was actually a volt meter calibrated in rpm.  I don't think you can use that tach without its matching sender.

John - "The Hoosier Hurricane"

Just found old sun tach i believe no numbers on it just a image that sun uses on front.  It about 2.5" dia when removed from case only has to post one marked + the other - . nothing else.  Look very nice and would like to put it in my Crown with a y block.  But have no clue how to test it.  Do not want to fry it.  Anyone ever seen one and know how to test it?  Or is it going to end up shelf art.  I will post picture later.