1999 Park Avenue Electrical Problem

Hello all,

I have a 1999 Buick Park Avenue with 100,000 miles and recently
experienced an electrical problem.  Hoping someone here might see the
connection between these symptoms.  This all occurred at the same
time.

1. All interior lights stopped working, except the ashtray convenience
light.  Trunk light also inop.  Cannot turn reading lights on with
switches, and cannot turn on by turning headlamp knob,

2, The "Battery State" display indicates "????".  I replaced the
battery with a new one.  No change in the indication.  When starting
the car, it first indicates 0 volts, then changes to ????.

3. The computer readout for MPG, average fuel consumption, and
remaining range are off.  It shows I go through 35 - 40 gallons a
tank, and the average fuel mileage is very low.  I still get the same
gas mileage as before.

4. The rear window defroster button beeps when pressed, but does not
light up and the window does not defrost.

5. The air conditioner compresses does not engage when running the
A/C.

6. If I have the keys in the ignition with the door open, the alarm
does not beep.

This started one night when I unlocked the doors with the remote and
the interior lights did not work.  When starting the car, the "Service
Vehicle Soon" light illuminated and the air bag light stayed on after
flashing the normal amount of times.  I had the service light checked
and there was no error code.  The Service Vehicle light went out the
same day, but all other problems remain.  

I believe I went through all the fuses and they looked good.  

Any ideas?


Thank you in advance,
Igor