Looked through posts on Vans Airforce and concluded a 1/4" hole through the rear bulkhead was OK. The grommet around the 3-conductor/shielded cable grips it very tightly. Used a small socket to put enough pressure on the grommet to drive it home.
In Image1, I've routed the wire to an Adel clamp that directs the cable veritcally. The cable (inside the corrugated plastic anti-chafe) will loop around beneath the bottom rudder brackets then down inside the rudder's fiberglass bottom. Rudder motion will thus impart a mostly twisting motion to the cable to promote the least possible fatigue over time.
Image 2 shows a separate 20 ga wire with a ring terminal under the AN3 bolt head, pn top of an AN970-3 washer. The bolt, terminal, and washer were coated with dielectric grease. The negative probe from a multimeter was used to test continuity to the airframe. Also tested with the neg probe attached to the other end of the wire: resistance was a < 1 Ohm with the pos probe on the upper fuselage skin.
The separate wire runs along the cable and is terminated with a crimped ring terminal (with it's ring snipped off) to the cable's shield, shown Image3. The last bit of the wire had a Molex pin crimped to it, as did the 3 cable conductors. The cable reaches all the way to trailing edge of the rudder: more than enough to unscrew the position/strobe light and disconnect if needed down the road. I'll add heat shrink around the Molex connectors to make sure everything staus together.
Tail light cable emerges from rear bulkead
Local gnd wire will be bonded to cable's shield
Completed connection; to be secured with heat shrink