12/240v lighting?

I am only guessing and trial and error without proper test equipment. I assume as you say it blows fuse we are talking 12volt system.
Without plugging into mains..

First if fridge 3way type 12v 240v and gas ensure 12volt switch is off try lights. if blows it's not fridge causing it. Then try another light after replacing fuse unless you've done that already.
Next check wiring at 12volt fuse box.
Next check the charger feed although if that was faulty it's own fuse would blow.
Check the battery by substitution use a car battery [Temporarily] just to test as it could be battery internal fault arising under load ie when turning light on.
If one particular light causes it then replace light it may be internal fault. Without test equipement it's trial and error.

Bob
May 2009