A3M XLR connectorA3M XLR connector
A3F XLR connectorA3F XLR connector

A3M (cord mount, male) and A3F (cord mount, female) showing pin numbers. With reference to a tip-ring-sleeve plug, Pin 1 corresponds to the sleeve, Pin 2 to the tip, and Pin 3 to the ring. Pins 2 and 3 connect to leads that carry the audio signal, while Pin 1 connects to a grounded shield. Chassis mount XLRs are C3M (male) and C3F (female). Pin numbers are identical. The illustration below shows a properly designed XLR to TRS adapter cable.

XLR to TRS adapter cable