Label a switch terminal "1".
Find a terminal that has continuity to 1 and label it "2". Label the other two terminals 3 and 4 and check that they have continuity and
that there is no continuity between 1 & 3.
Flip the switch lever:
if there is now continuity between 1 and 3 there should also be between 2 & 4 and none between 1 & 2.
or
if there is now continuity between 1 and 4 there should also be between 2 & 3 and none between 1 & 2.
Find a terminal that has continuity to 1 and label it "2". Label the other two terminals 3 and 4 and check that they have continuity and
that there is no continuity between 1 & 3.
Flip the switch lever:
if there is now continuity between 1 and 3 there should also be between 2 & 4 and none between 1 & 2.
or
if there is now continuity between 1 and 4 there should also be between 2 & 3 and none between 1 & 2.