Microphone Jack Troubleshooting

I'm having issues with the pilot-side microphone jack in my recently purchased RV-6A. When we flew it home after purchase, the microphone on my Bose headset wouldn't work. I was able to swap it out with an old mono headset, and the microphone worked OK, but the hearing was awful. Once home we tried to diagnose the issue. We ordered a new microphone jack and soldered it in place of the existing. Now the issue is this: with the insulated shoulder washer in between the jack and the mounting plate as it is supposed to be, the microphone still does not work. If I remove the shoulder washer, the microphone works, but the jack cannot be properly tightened and there is terrible and constant popping in the headphones (I'm presuming from electrical interference). Any ideas on why the microphone will not work with the shoulder washer in the correct position, but will with it removed? What am I missing?

You're missing ground (shield) continuity from the barrel of the jack to the intercom (or radio, if there's no intercom).

Remove the jack from the panel, so it's floating in air. Use an ohm meter set to its lowest range. Touch one lead to the barrel (threaded portion) of the jack, and touch the other probe to the case of the intercom or radio.You should get near zero ohms. Odds are high that you'll see an open circuit.

Follow the wire (might be the shield) that's tied to the barrel terminal, back to the intercom/radio, to see where it's broken, and repair.

Charlie

That is puzzling! I'm no expert here but my first thought was something in the wiring elsewhere in the jack/intercom system or maybe a short. I wonder if this is a new problem or has it been ongoing. Electrical problems are the worst.... like chasing a ghost.