With the fuse back in, pull the cig lighter out and see if it's warm.
If so, you've found the drain. The cig lighter and radio are normally
on the same fuse (that's still powered with the key off), to keep
the radio memory alive. You can also unplug the cig lighter to see
if the drain's in the radio.
Auto mfgs try to keep the key-off drain around 7-15 ma, to allow
a battery to start the vehicle after 30 days. This is good for long-term
parking in airports and such...