I do 80% Electrical Diags at work. they are a pain in the ass!!! but a huge satisfaction when u find the issue. anyway man it can get costly specially with shops charging fro 92 bucks an hr and up. specially if u get into flow chart charge. THEN your in for it. but your issue sounds pretty straight forward.

anyway what i would do is get a schematic and follow where ever there's a junction box/circuit breaker/or connectors.

for example if the circuit has two connectors first one by the drivers seat second by the trunk. what i would do is disconnect he first connector. Plug a fuse in if it blows you knows it is pass the the first connectorif it doesnt then it is from the that service connector to the fuse box. brkae it down keep it simple.

another thing u can use is a multimeter. or power probe. look for continuity with ground.

also if you use this tactic i would disconnect the light bulb im some rare occasion i seen a busted bulb cause this same issue. also bad or corroded pig tails.