How to further pinpoint lighting circuit short

Continuity may not be meaningful since a single bulb etc could have low resistance. Have you connected 12V to the circuit and a fuse blew?

If you actually have a short what fuse blew? Add a light bulb in series to that circuit and it will be full brigntness with a short. Then as you open downstream wiring and when the light turns off you can isoate the problem and resolve as needed.

And a wire tracer can be very useful in determine wire routing.