Started yesterday but entering all time this entry. Fabricated a mounting plate for .050” aluminum to support the ELT mounting bracket securely without flexing or vibration. It is riveted to the Station #4 bulkhead and two of the stringers on the floor of the tailcone. I couldn't bend a double offset in that thick of material so the front support is a piece of 1/2x1/2 angle with countersunk screws coming through from the underside of the fuselage. When finally mounted, it is very solid.
Next was the D-Sub connector which actually required a fair amount of soldering. There is a g-switch loop to connect, power and ground for the piezoelectric buzzer, a ground wire to the airframe, and three wires from the Steinair harness (2 for switch and 1 for gps data) for a total of 8 connections on a solder cup type of D-Sub. I made it work nice, but would consider buying a crimped pin D-Sub if doing it again.
Fabricated a doubler for the ELT antenna to rivet to one stringer on the roof of the tailcone and lay against the skin where the antenna will mount. Secured the antenna wire around the back side of the station #4 bulkhead with clamps and tinerman plates/screws. Burned more time than I anticipated, but it all looks good and panel switch did work correctly.