There's one more thing that no-one has directly mentioned .. I spent many hours trying to trace an intermittent fuse blow problem (only with lights switched on) a long time back ... On a crappy Montego.

It turned out to be a short (only when warm) in a backlit switch in the centre console .. namely the Electric LH window. So try isolating backlit switches, too ..
including the Lighting switch itself (in some way) Takin out the bulb, aint enough, obviously!

Pain-in-the arse prob this