replacement radio, 02 pontiac sunfire

I have a 2002 pontiac sunfire with the basic Radio/Cassette player. I want to replace this with a used radio/CD player from another sunfire. my radio/cassette player has one 24 pin connector. I noticed the radio/CD player has one 24 pin connector and one 12 pin connector right next to it. What is the 12 pin connector for? Will the radio/CD player work in my vehicle if I only have the 24 pin connector wire?

Provided the replacement radio is for a Sunfire, it should work, but it must be set up using a GM scan tool (Tech II). The extra plug is not used unless the radio is for a late model car. It would be for the Onstar system to work through the radio.sparky

is the set up with the GM scan tool for the theftlock?