Audio Systems: adding, ford ranger edge, ford ranger

Question
My friend has a 2001 Ford Ranger Edge...It came with a 6 cd/radio...He wants to add a vehicle stereo with a cassette deck without removing the original one...can this be done?

Answer
using a auxiliary interface to feed the signal of the other stereo in to the factory cd6 stereo yes it is posibble,
press the cd button on the radio when the cd is playing you need to see
NO DJ NO CD and it is posible ,,if the display only blinks
that option is not available