The suggestion to check for the glovebox light is solid.
There's also the trunk light and You can pull a battery terminal
and place your multimeter on 10 DC amps and connect between the cable
end and the battery terminal (series connection) Then measure current with the car off. (WARNING: Don't try to lower a window or start the car because then you'll trash your ammeter/fuse)

You will normally have some low current flow: the clock, ECU, etc. and it varies,
maybe 20-25ma is normal. If there's a light on somewhere then the current will be higher, you can pull fuses to see what circuit is drawing extra unwanted current. It's also possible to have current flow in an unfused circuit, such as
the alternator, but start with the fused circuits first. You simply pull the
fuses, one by one, and see when the current flow drops down to 20-25ma.

Be careful to do the tests without engaging headlights or turning on the ignition.

Bill