It's good to correspond with you again. You may not believe it even if you remember the thread I'm referring to, but I took your advice; removed my luggage rack and mounted a hi quality dual band antenna directly through the roof of my '03 4Runner. It works superbly well. Now on to my newest challenge.
Yes, the TM-G707 uses an 8 pin modular plug.
1. Up button on mic
6. Mic low (same as ground on pin 3)
7. No connection
8. Down button on mic
I ran a standard LAN cable from the radio to my center console where I mounted a terminal strip. On those same terminals, I connected a Kenwood LAN cable and ran that from the terminal strip to a convenient location where I can plug in the mic. Now I disconnected terminals 5 and 6 comming from the radio and ran those to the common terminals of a DPDT rocker swtich. To one of the other sides, the wires run back to the mic connectors on the terminal strip and the other pair of wires runs from the switch to the headset mic jack. BTW, pin 6 is a shield covering pin 5 (mic audio hi).
Everything works as long as the headset and microphone are NOT plugged in at the same time. When they are, the radio keys as soon as I switch over to the headset. The Heil headset uses two jacks: a 1/4" mono jack for RX audio and a 1/8" mono jack for mic audio. I've since disconnected the RX audio line in order to focus on the mic audio problem.
I've checked the voltage, on the terminal strip, between the PTT and ground terminals. The voltage, while in receive mode, is 3 to 3.2vdc. When transmitting, whether with the foot mic switch or switching over to the headset jack while the mic is still connected, I get the same results: a voltage drop to about 0.15 to 0.17vdc. How can I isolate the microphone so it doesn't pull the PTT line down when I switch to the headset?
I've ordered a schematic for the mic and I'm hoping it will shed some light on this issue. A couple of other points: ground and mic low are electrically the same according to my ohm meter. Also, other sources claim that the PTT switch is electrically in the mic hi line and RX audio and mic audio share a common ground (return). I have some diagrams, but I don't think I can attach them here. You can see them at G4WPW site:http://www.qsl.net/g4wpw/date.html
Scroll down the page until you get to Kenwood most popular connections diagram. This is all I have to go on.