Snap-on bought SUN; you might contact them and see if they will send you a users manual... some here have had some luck with contacting them.
You never know; worth a try:
Snap-on Equipment Service:
For on-site equipment service, parts, technical support for Snap-on, Sun, John Bean
USA: 800-225-5786
Canada: 800-225-5786
These guys sell some replacement parts; maybe they have some manuals too?
http://www.centurytool.net/MT326C_Snap_On_Growler_Armature_Tester_Parts_List_s/374.htm
Found this on another page:
Sources of Info
Sun is now part of Snap-On. Bill Larsen of Snap-On's Equi-Serv division has been able to provide copies of a couple of manuals. No, they no longer have any parts for this old stuff. Bill's email address is
[email protected]. Bill has referred me to -
Roger Kunz ( I've got to ask Roger the name of the company he works for) has been authorized by Snap-On to service the old equipment. Roger's phone number is (815) 344-6538.
This guy is a vintage Sun fan; he might have a manual too!
http://bambam.gmu.edu/sun/index_files/Page1375.htm