Originally Posted by PulpFriction

If you have a factory subwoofer you have the Pioneer Premium speakers. That system has an amplifier behind the subwoofer that powers all the speakers. The means it needs an audio out signal for each speaker. I’m going to guess that each factory radio that was compatible with both the base and the Premium speakers had both a speaker connector for connection direct to the base speakers and a signal out connector for the Premium amp, and that you only connect one of them.

Originally Posted by donbrew

Some radios have a cooling fan, depends on the vendor GM used a few different ones.