Another way is to disconnect all the small wires from the battery (with everything off).
Touch them individually to the battery. Any sparks indicate current draw. Although not scientific, a rough guide is
small orange sparks - small current draw
Larger orange sparks - more
Small blue sparks - more current
Larger blue sparks/audible click lots.
Now don't laugh at me, but it is a quick and easy way to work out which wires are worth a second look with a multimeter.
Another option is to put in a solar panel. A small type that plugs into the cigarette lighter might do. Any larger panels would need a solar regulator.
Another option is to refit the battery with another cranking battery. It will last twice as long then.
(and of course these options are merely masking the problem).
