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.