99 cavalier Smoke coming out from under dashboard!

Sounds like there is an electrical problem. Its probably in the ac / heat system. I would suspect the blower motor resistor or blower motor is going bad.

This could be a serious problem if the smoke smells like plastic or has a metallic hint ( I.E. You have a metallic taste in your mouth after smelling the smoke).
Remember the old adage " Where there's smoke, there's fire".
If you don't know how to disassemble the dash to find the problem, take it to a shop A.S.A.P. - You could burn up your vehicle by using either the heater or defroster, as they are parts of the same system.
Now for the rear defrost light;
If the light is out but the defroster works, you possibly have a burnt bulb. You'll need to remove the panel the switch is mounted in to gain access to the switch. You'll probably have to replace the switch to repair that bulb.If neither work, then you likely have several electrical issues that need to be repaired.
Sorry to bring bad - ish news!!

the bearing in the blower motor is going out causing the noise and the smell is coming from the blower motor. the parts house will give you the right blower motor for your vehicle make and model and engine size.

Faulty blower motor, or relay, possibly bad blower motor or resistor. Can possibly be bad blower motor switch.

Check you cabin filter it is under hood on pass side near wiper blades
If the blower motor is running fine and no smell from there.

If the blower motor is still working, that was not the problem-the strange smell might have been from some bacteria in the plenium, and the smoke may have just been the result of condensation from the evaporator in the plenium-keep an eye on it, but if the blower is working, I would not be overly concerned about it.

sharp acidic smell would be electrical
sweet smell would be coolant.

Smoke from under the hood ?
Smells like burnt rubber ?
Either the compressor or the comtressor clutch is bad so it locks up wen you urn it on and the fan belt is burning..

have the ac system inspected..

either something melted in the housing from the heater core or the blower motor went bad. It could also be that there is a crack somewhere in the ac line.

what does it smell like? antifreeze, burning wires, oil, no smell, here is my best guess, 1- heater core, 2- heater blower motor burning up, 3- engine oil, and 4- steam condensation, 5- a ghost.