Lights Out
Just sitting here thinking about your problem.It doesn't seem that the odds of a broken wire would be too great unless you have recently pulled new wire through the same "chase." But, I would think that corrosion could be high on the list of suspects; a salt-air environment, seepage of some salt into little cracks and crannies from 20 years of washdowns, etc. I would start at the panel with the breaker for the "Cabin Lights" circuit. Remove it, Use a small wire brush to make sure the bus is clean and take a voltage reading there, likewise, clean the breaker mounting tabs and wire lugs. Re-attach the breaker, take a voltage reading off the breaker, whether the reading is low or normal, exercise the on-off switch handle a few times, check with the meter after each test to determine the functionality. the last test is to short out the breaker to insure it can satisfactorially open on a short circuit - the basic reason it is there. Use a heavy (10g)insulated wire. Touch it to both the hot and neutral lugs. If the breaker does not immediately pop, internal corrosion has probably damaged the breaker and it needs to be replaced. Corrosion inside the breaker can partially or totally destroy its functionalty.After the breaker has been checked out, take a continuity tester and check the circuit wiring from the panel to each of the lights giving you trouble. Extend the leads with lamp cord and insulated alligator clips. Check for clean wire at all connections. If that has not solved the problem, you will have to find the location in the chase where the wiring for the head and forward cabin tee off. This is another place where corrosion could have degraded the continuity of the circuit.Have fun, if this isn't fun, make friends with a competent electrician!