Voltage leak?

Yup.

Disconnect the battery ground clamp and put a 12v test lamp in there. If you can't see it, get it in the dark, shade, etc and look for a glow. Start checking and unhooking "stuff," and fuses.

The alternator is not hard to find, LOL, just unhook the main wire at the alternator stud and see if the light goes out.

If you don't see a light, double check with a multimeter on current (amps.) Be CAREFUL to check with a lamp first, because if the draw is too much, it can pop the fuse in the meter. Be sure to start with the current setting on the meter on it's highest range and work down.

Don't forget the lighter, glove box/ trunk/ underhood lights, etc. If you have a newer radio with a "memory" wire, (keep alive) suspect that, as well as any radio/ stereo/ amp that is wired "hot."