I didn't ask for permission to cross post this, so I'll just pass on the Gist of it from a highly experienced pilot on one flight.
Best,
Dave
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Seems that the transponder started changing codes rapidly when he was on an IMC departure in busy airspace. He declared an emergency when all electronic went out....
My first mistake was to try and fix the transponder, and switch to #2. In the G-IV it takes a single switch (1 <> 2) to do that, but this wasn't the G-IV. To do this in the Eclipse you have to go to the MFD (center display), select a page, select the transponder function, and select the number 2. (Memory fades, that may not be precisely correct.) It's a real handful in the heat of battle, and I was near saturation. Remember it was rough as hell, getting dark, and solid IMC.
At that point there was a total electrical failure for an instant, then it came back on with all attitude indicators showing big red X's, the autopilot kicked off with the airplane badly out of trim and worst of all, every audio warning (I think there's 13 of them) and radio volume came on, and went to full, maximum, excruciating volume, and the volume control didn't work. I had only Com1 selected, but I was getting ALL radios including the VORs, AT FULL VOLUME. I've never in my life been exposed to such a ear-splitting cacophony of noise. Somewhere in there I heard my "buddy" yelling at me about heading and altitude, but he was the least of my worries. I did declare an emergency, but he may not have heard it. After a few seconds the emergency gyro came back on (or maybe it stayed on and I was just so disoriented by the noise that I didn't see it) and I went to wings level, hoping it was correct.