Not really a diagram, but a sketch borrowed from an unknown source.
Problem: Heil makes dozen of different headsets. There are dozens of big radio manufacturers, each brand having their own unique microphone input circuitry. And even within a same brand, there is more than one input connector.
Heil’s solution: a radio specific adapter called AD-1.
You pick your headset. Then, you buy an adapter to suit your radio brand: Icom, Kenwood, Yaesu, Ten-Tec, Elecraft…
Have more than one radio brand in shack? Just buy another adapter, keep the same headset.
Literally plug and play. The second connector on the AD-1 adapter is for “PTT device”- either hand PTT switch or footswitch. Sold separately.
Now, the exception to above: headsets for hand-held radios. Heil calls them HTH and they come with pre-installed mic and PTT connectors. Not good for your big box radios.
As you already know, headsets for Icom radios are different than Kenwood and Yaesu (different microphone element).
Please always specify your radio brand and model when ordering a headset. AD-1 for IC-7300 is different than AD-1 for IC-705.
As said before, if we work together on this, there is a good chance we’ll get it right on the first go. And if we don’t we’ll get it right eventually.