I do not have service info for your car, but i will try to answer your questiuon.
You say the door chime and headlight warning have stopped working,, it seems to be ( and i get this info from other gm cars that have similiar systems ) that the warning buzzer module may be faulty,
,,on some cars it is located under the steering wheel or in that area of the cars interior.
If there was a " short " you would be blowing fuses.
The chime,door switch/radio, headlamp warning are all tied into that buzzer module.
On some car it buzzes or dings or rings or makes a sound of some sort.