Here are the steps you need to follow in order to mute the second handset port on an RJ9 Y splitter.
1) Open the splitter enclosure
As shown in the picture below, use a small flat screw driver to apply gentle pressure on the 4 corners of the enclosure. You may need ot do this little by little to avoid breaking those brackets, however if you break them, don’t worry, you can always use crazy clue to glue it back together after you are done.
2) Identify the secondary jack. This is the most important step! If you cut the wires on the primary jack, you will disable the ability to talk on both handsets.
The secondary jack is the one that has the wires coming from the primary jack. The primary jack has the wires coming from the cable.
Why do you want to cut the yellow and black pair?
The diagram below shows the wiring on an RJ9 jack. As you can see the yellow and black wires are used to transmit (TX) your voice. This pair is also referred as the “Microphone” pair. This the pair that will cause your handset to go ‘MUTE” when disabled. By cutting it you will disable the functionality of this pair.
4) Close the enclosure and seal it.
If the taps are no longer working, use crazy glue on the borders to keep it together.
You may want to identify the secondary jack using some marking or label.
Congratulations! You now have a n RJ9 Y Splitter with a MUTED jack! Simply plug it back in your phone and start using it!