Connect the Leitner connector cord (green tape) into the green TEL port
Flip to the bottom of the base and ensure the left switch is set to RHL and the slider is set to 1. (Set the slider to 4 instead of 1 on Cisco phones if your Cisco phone has a Headset port in step 4)
Check the back of your phone for a Headset port. If it has one, plug the Leitner connector cord into that port, and you’re done
No Headset port? Unplug the handheld receiver curly cord from the Handset port. Plug the Leitner connector cord in its place
Plug the receiver curly cord into the far right port on the back of the Leitner base, then you're done!