Can you wait to try each suggestion over a few days? Instead of relying on trial & error, or "The Usual Suspects" (really great movie, but here I'm referring to the suggested door locks, etc.), I suggest this.

First, indeed, 100 mA is indeed high. As a matter of fact, the normal drain for a 1993 is much less. I have two '93's, one with a clock and one without (tachometer in its place):
-- without a clock, a steady 7.8 ma (i.e., 0.0078 amps), and 2.8 mA of this is just for the radio's preset memory.
-- with a clock, ~12 ma with pulsing briefly to 25 ma for the clock's motor.

Since you specified 100 mA rather than just saying a "big drain", I'm going to assume that you already have a digital VOM. If not, buy a cheap one at Radio Shack -- it's good to have. And I'm glad that you know enough to measure your drain between the negative terminal of the battery and ground, instead of between the positive terminal and the cable, which is a dangerous technique (everyone should always remember when disconnecting a battery to remove the negative terminal first, and alway connect a battery by attaching the negative terminal last).

Okay, let's start at the fuse panel. The idea of this "track down" (wasn't that an old TV western from the 1950's? Gives you an idea of my age :-) is to identify the circuit where this excess current drain is being drawn. First, get something (e.g., strong tape) to block your door open switch (you don't want to falsely blame an innocent circuit) so your dome light, etc. isn't reacting to an open door (switching off the dome light at the fixture is not helpful, because the drain could be in-between). Next, with your VOM's probes ready, start removing fuses at the panel, one at a time, and putting your probes across the empty terminals.

You should find the main circuit with the drain by the above. Then, and this is harder, you have to break down the branches of the suspect circuit into its components and check each one the same way. I can't explain how to do this, because each is different, but I'll bet its intuitive to you by now.

Good luck.