I have one of these from a collection of Pre-War tinplate miscellany I was given.
I find that there were two configurations for the #91 of this era. Mine is configured as shown in this file photo...
Question: How does one wire this up and test it to determine whether it's functional...i.e., will break circuit??
The only info I've found is re the later Post-War model under the same number...completely different.
Thanks for the help!
KD