Larry, if the coax connections and antenna are good (might try using a handheld at 5 watts through the V6 coax to its antenna and TX to another radio) for a TX test, and recieve is clear it's either a Mic issue or a V6 radio issue.
If you would like when I get back from Oshkosh I'll send you a V6 test radio complete wiring harness that you can plug into back of the radio, then use your or any standard headset and just provide temporary power to it. This way you can do some more troubleshooting to separate radio from A/C wiring.
Just let me know.
RV-8 Under Construction
Flying RV-6A with Son Chris
IO-360, MGL-EFIS, G430W, NavWorx ADSB
2017 Dues Paid, Home Field 18FD