Interesting timing! I'm troubleshooting my nonfunctioning bow light on my 306. I don't have continuity on the negative wire and am having trouble figuring out how/where the negative wire terminates in the breaker panel.
Generally, the wiring runs along the inward facing lip at the bottom of the port-side hard plastic headliner wall panels. It feeds into the breaker panel at the corner by the head bulkhead. The route through the bulkhead from the v-birth to the saloon is tricky since it is hidden behind the hard headliner walls. Similarly, access to the breaker panel is also constrained by the headliner. It would seem that the only way to get access behind the hard headliner wall, is to first pull down the soft headliner ceiling, which looks to be a project unto itself.
I did find a tan colored "wire" that I mostly ignored which was run alongside and bundled with the bow light wires, and which ended about halfway up the v-berth. I wonder if it wasn't the messenger that Don mentioned? But the only way to access it is to first remove the forward wall of the v-berth and then man-handle the bow light wires to pull the bundle down from the headliner wall.
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