What specific part causes several electrical parts to fail at the same time?

What is your question?

Trip odometer, dash clock, interior dome lights, head lamp relay, gear shift lights, auto seat adjustment all stopped working at the same time. Also, when I turn on my engine the air conditioner always comes on set at 75 no matter what setting I last turned it to. I have no way to tell, so I wonder if the air bags also are affected.