[Elecraft] K3/K3S Pin 1 question

[Dan Atchison via Elecraft]

I am building a switchbox to allow use of a Heil PR-781 microphone to be 
used by my K3S and K3, the switchbox using XLR connectors.  I note that 
in the Heil XLR cable ended in an 8-Pin Foster has mic low (-) tied to 
ground and (+) tied to mic high.

Knowing that the XLR pin 1 should be chassis ground, my question is, "At 
the switchbox, should I tie XLR pins 1 and 2 together and only switch 
XLR pin 3 between radios?"  IOW, should XLR pins 1 and 2 be chassis 
grounded or should I chassis ground pin 1 and switch both XLR pins 2 and 3?

Thanks in advance.

73,
Dan