Help in diagnosing a problem

[Tmacmi]

I have a series of cabin lights along the port side.

Lets call them A,B,C, Ca, D, E (Ca is a light spliced into the C wires with those bayonet splices)

These are standard 12 v bayonet bulbs

I believe they are linked in parallel on one circuit. (I can visually confirm that at least B and C are)

Lights C, Ca, D aren't working. The remainder are.

I'm trying to track down the break in the wire is on the positive or negative wire.

In order to track it down I put the continuity leads on the outside housing (-) of the bulb housing on B and C. There was no continuity. I did the same for the inside bottom positive, while pushing all the way to the bottom of the housing. Again no continuity.

In order to confirm my logic in testing. I did the same for lights A and B, which work and they didn't have continuity either.

What am I missing?

Thank you

[TrentePieds]

Trying to test for continuity via the sockets is dodgy. Make up a longish #12wire with crocodile clips on each end so you can reach from one end of a circuit to the other even if the distance if forty feet.

Pull the light fixtures off the bulkhead(s) so you an get at the terminals where the wires connect to the fixture. If the fixtures have "tails" that are joined to the circuit with crimp fittings, replace the crimp fittings with terminal blocks. Quick and dirty schematic attached.

It'll take you an hour or two to do that job, but you'll never again be in doubt about who is doing what and to whom and you will always know where to put your probes to test for continuity AND for voltage:-)

All the best :-0

TrentePieds

[Spot]

Tmacmi,

-Which type of bulb? A BA-15-D does not conduct through the case like a 1156/1157
-Are there 4 wires coming from each socket/fixture or only 2?

I would have suspected the 'add on' clips cut power or ground but that would not explain the 'E' position working