I don't have the diagram but here is my guess. I would think the only thing not fused is the starter. However, you could have a relay that has failed (stuck closed) so that current is being drawn from the battery all the time. You might try pulling the relays one at a time to see if that isolates it.

You should be able to do this by watching the current drain with a meter (what are you using to measure it?) while a battery charger is on the battery.

The other way is to feel around to see if any thing is warm to the touch.

How much current are you seeing? It has to be more that 15 or 20 amps because otherwise your battery would stay up for 5 or 6 hours (per the amp-hour rating of the battery).

That's why I wouldn't think it is a dome light or truck light as those don't draw that much current.

Keep us posted...as these are interesting problems.

Joe