I've got an electrical problem somewhere and hoping someone can help me
diagnosis.  Basically, only sometimes, the battery looses voltage and won't
start over a period of 8-10 hours--there is a drain or a short somewhere.
These are the only circumstances that have changed since this problem arose.

1.  Hit a deer, wrecked the radiator and radiator fan, which I replaced.
2.  Installed a radio cassette player.

How can a multimeter be used to identify the source of the drain?