My '89 convertible had a leaking heater core so I replaced it myself.  I had to remove a lot of items and moved around a lot of wiring.  Now several items don't work:
- the courtesy lights and rear trunk lights do not come on when the doors open
-the heater, air/blower/blend doors do not work (electronic controls)
-the Bose radio and antenna do not work....however the cassette player will play, fast forward and reverse (with no sound)
-one time the car would not start...no power to the starter but the digital dash did light up when the key was turned to the start position
-the digital dash works, but the gauge showing 'range' (distance in fuel remaining) shows 0, or climbs up and down slowly before finally settling in on the correct reading
I've double checked all the fuses and any connections I might have disturbed, but did not look behind the fuse panel or deeper under the dash towards the radio.
Any suggestions?

As you may have guessed you need to go back and check all connections as well as fuses.