A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Bill Morris
Date: 2021 Mar 8, 15:06 -0800
If you look at the bulb, you will see that the tiny glass lamp is separated from the threaded brass base by insulation and there is an annulus of white metal surrounding the glass (in fact it is the end of a bush wthin the insulation). One lamp wire is attached to this annulus and the other wire to the threaded brass base.
Looking now into the depths of the bulb holder on the sextant you will see a disc of white metal that is separate from the female thread. When the bulb is screwed into the holder, the annulus surrounding the glass lamp makes contact with this disk and the circuit is completed via the body of the instrument and the brass base.
When you further deconstruct the lamp area (two screws and the ground glass shade comes off too), you will find a wire going to a solder tag that is part of the disc. If there is a short circuit, someone may have been there before you or the short may be elsewhere in the circuit.