what is the name of the part in the door that shuts off the radio when you turn off the key

It's built into the door latch assembly.

Switch? Do you mean after shutting down the engine in the car, the radio continues to play for a few minutes, and when the door opens it shuts off? There is a switch either on the door post or connected to the door handle inside the door. I have a 2004 high mileage Buick and my switch at times sticks and will not turn off the radio. I have to either slam the door, or open the passanger door to get it to shut off.

2006 Impala: The switch that turns off the radio and accessories when the driver's door is opened after the key is off is in the latch assembly. Mine works sometimes. When it does not I use my key with the door open to manually close the latch in the edge of the door two clicks and then push it a little farther to the stop. Then I lift the outside door handle to release the latch. This has always worked to turn off the radio, when slamming the door would not.

To ath math you were absolutely correct! It worked my dad took the car to the Chevy dealer twice an they couldn't figure it out! We would have never tried all that I'm glad I found your answer