Battery runs down overnight

[kjh1997I30]

Vehicle: 1997 Infiniti I30

Symptoms: Battery is dead by morning

The battery is a 2 month old NAPA and runs down with the ignition off. Tested good and recharges good. Alternator puts 13.5 volts into it when running. Removing the negative cable and putting a test light between the negative post and the negative cable indicates a short in the electrical system (i.e., the light comes on). If you open the narrow fuse box under the hood next to the battery and pull the Battery/ignition fuse (big one at the top of the box), the light goes real dim--but that's the circuit that powers a lot of stuff, so not much help. None of the other under-hood fuses cause the light to go out or dim. If you open the interior fuse box and pull the top/middle fuse labeled "ROOM/L," or "ROOM/I," (can't tell if it's an L or an I) the test light goes real dim. Not all the way off though. This fuse is apparently for the switched overhead light inside the vehicle near the sunroof switch. With the fuse in, the overhead light isn't coming on and staying on unless you push the on/off button--which is exactly what it's supposed to do. When you turn it on and off with the button, it comes on and goes off like it's supposed to--but it doesn't pop the bulb or the fuse, which indicates to me there's no short. However, the circuit is drawing current all the time.

In any case:

Questions: Why doesn't the fuse pop or the light bulb pop when power is applied? If there's a short, it seems like it would.
Also, if there's a problem with that circuit, why doesn't the test light go off all the way when the fuse is pulled? Could there be a problem in another circuit too?
So, how to fix it? Any idea where this circuit could be draining current, i.e., is this a common problem that anybody else has had? Also, does anybody know where I can get a a free wiring diagram?
Any help appreciated.

Keith

[kjh1997I30]

The fuse is definitely labeled "ROOM/L." Just had to rub some dirt off the cover.