The big antenna plug you plug on the back. I dont know the brand of your stereo (sometimes the color coding changes), but there are two wires that power other accessories on some aftermarket radio. In the case of Sony, on our products the blue wire is the antenna remote (is what signals the electrical antennas to rise and lower the antena), and the blue/white wire is the Amp remote (tells the amp to turn on). If you do not have an electric antenna or an amp, just leave those two cables disconnected (and tape the ends to avoid shorts!).