The ICOM IC-92 radio comes with a waterproof connector for external mike and speaker. The connector itself is proprietary item that I could not find as an individual item to buy. As I made a custom headset and PTT button circuit myself I needed to connect to this jack on the IC-92. The programming cable is not suitable here because only 3 wires for programming are attached on the connectors. Buying (another) external microphone HM-175GPS was not taken into consideration due to the price.
I choose to buy a replacement part OPC-1755. That is basically the microphone cord for the HM-175GPS. Before building my circuits I made a few measurements to identify the pinout of the IC-92 connector. That lead to 7 of 12 pins beeing identified. A comparison to the OPC-1799 showed 3 other pins that are in use for programming the radio. Even GND is different for the programming and the microphone cable. In the end I could identify 10 of 12 pins on the connector of the IC-92 radio. The others are abiously not in use. For the wiring I made a little schematic shown in the graphic.
Please be aware that any modification to your radio may lead to a loss of warranty. Use this information at your own risk. I am not responsible for any damage to your equipment.