One problem related to alternator/generator/regulator has been reported for the 1999 Buick Lesabre. The most recently reported issues are listed below.
Battery went down when clock left on because ignition was loose or faulty. So now I make sure clock is off when I shut it down. Car started up fine - drove it 6 miles - came back out to start it after an hour and nothing-no sound nothing-about 20 minutes later I tried it again and it started right up. There has been a grinding sound n cassette player with no cassette in it at one time. Dash lights lit up while driving so automatically thought there is short in dash board. Second time I put key in and nothing happened-no sound-nothing, when it finally decided to start this time I took to auto zone. First they said battery, but battery is pretty new, then another man said alternator. Got alternator from shop that rebuilds alternators and they don't think it is alternator. Rear defroster doesn't work and for some reason I think short or problem could be here, but not sure. I've driven it many times with dash lights on, knowing that nothing is wrong with car. Oil is good, cooling good, transmission good. It has to be an electrical problem. Alternator belt is not loose. Todate, the problem has not been fixed. I even thought it was key, so got second key and tried it - not the key.