The exterior lights are really suspect units. The light socket sometimes do a direct short to ground. I would remove the light fixture lens and inspect the bulb and socket. Sometimes the bulb itself is the culprit. Just remove the bulb and see if the short goes away.
My popup circuit 12VDC used to feed my front porch light, my AM/FM radio circuit, propane detector on the floor, and battery monitor meter all on the same fuse in the 12VDC distribution panel.
My 2008 POPUP originally had the ELIXIR Converter/charger unit which only has four fuse circuit and one 120VAC circuit breaker circuit.

All of the 12VDC circuits coming from this units was on three fused circuits. These circuits were divided up by grouping many 12VDC lines together with those large yellow twist type wire nuts behind the ELIXIR unit. If yours is like this it should be rather easy to isolate the culprit.
I replaced my old ELIXIR unit with a WFCO WF8900 series 120VAC and 12VDC Power distribution unit. On the DC side this allowed me to have eleven separate 12vDC fused circuits and up to nine 120VAC circuit breaker positions.

This is a simplified block drawing showing how my WFCO WF8900 Distribution unit is being used.

Certainty makes it easy to identify shorted circuits having each line individually fused.
Hope you find you shorted line soon...
Roy Ken