I tried to plug the harness in to only the larger of the two but the harness I have is now too big for the one coming from the car.

I have an 05 Pontiac Vibe GT and am trying to swap out the factory stock one CD radio with a new Pioneer receiver. When I took out my stock radio, I saw that there were 2 different bundles of connection wires, one smaller and black, and the other one larger and white. I bought what I thought was the...