The most common way to wire a 3-pin XLR to a 1/4 inch (6.5mm) mono plug (sometimes called a jack plug), is to join the negative and shield together.
This can be done by either soldering the shield and negative wires of the XLR to the sleeve of the plug.
Or by soldering a jumper on the XLR.
Either way gives you the same result: An unbalanced audio cable.
MAONO is an innovative designer and manufacturer of Lavalier, Podcasting, Wireless, Shotgun, Recording microphones and accessories for Smartphone, Camera and PC, etc.