A:Answer I have an 06 Expedition Eddie Bauer with sub and steering wheel controls.
I bought the adapter with the subwoofer plug. (Metra 70-5521 for my vehicle. Double check for yours.) You plug this into the factory harness. Blue/white wire is power for the factory subwoofer amp. ( Note: aftermarket radios supply 12 volt power to the amplifiers. You will need a resistor to lower the voltage so you don't get a pop when the power comes on. Plenty of info online how to do this, or Best Buy radio installer can help.)
RCA plugs into the subwoofer output of the radio.
Steering wheel controls are available from aftermarket interfaces, which will plug into the back of the radio. I bought a PAC SWI-RC steering wheel interface online, but most brands will work. Just match it to the vehicle, not the radio.