Still inop, both lights. Confirmed the switch and fuse are ok by swapping cockpit light terminals with uw light terminals. At this point, wiring or the lights themselves must be the culprit. Blue/gray wire leaves the switch and disappears behind the bulkhead in the cockpit locker. But the wiring that emerges from each transom clamshell and running to the light is yellow, terminating in a waterproof sealed connection at the light. I guess the yellow wiring could actually be a bundle, with the blue/gray wire from the switch inside, and maybe a ground wire. (It’s not clear to me how the light is grounded). At some point, though, the blue/gray wire has to be split in order to reach the two individual lights. I have no idea where this connection could be, or how to reach it.
Anyone have any ideas on next steps?