Hi Geordie. You probably wont be able to get hold of generic wiring diagrams for the PTT and the interface to the intercomm and radios as these will have installed after the aircraft was delivered. The PTT switch will normally operate a relay to switch the microphone input from the intercom amplifier (if you have intercom installed) to the selected VHF transceiver. It will also provide a ground (earth) to the VHF transceiver to switch it to transmit mode. This can be via a bespoke relay switching unit or a propriety off the shelf unit. Your friendly neighbourhood avionics guy may be able to provide you with further information. You could also check back through your log books to see who installed the radio in you aircraft and ask them to provide the wiring diagrams from the modification.