This is Kevin from ReplacementRadios. There is no factory-type aux input available for that radio. Several manuacturers used to have it listed for their devices but they all pulled the Grand Prix because it was not functioning properly in them. Although it has the same plug as other GM radios from that time-frame and uses the Class 2 data bus, there is something slightly different about the Grand Prix and there were too many instances where it was malfunctioning. You can use something like the IS31 from our site that goes through the antenna jack. Just make sure you get the motorola antenna adapters too. They are an option at the bottom of our IS31 ad.
The cd/aux button on your unit , is for either/or. In other words, when there's a cd in the carriage and you hit the cd/aux button, the cd OR an aux input will be played. Since the cd player is hard wired into the amp circuit, that's what plays. And you would loose the cd player, if you had a hard wired aux input installed to the factory amp. Now, keeping the factory radio is advantageous for all the extra features it has. I recommend an inline FM modulator. An Audiovox FMM100 works very well. With this you will also need two Delco to regular antenna adapters, and a 3.5mm stereo to two RCA male dash mount plug. This is a bit involved to install, but preforms as good as a factory installed aux port. It needs power to operate, so a switch & the 3.5mm plug need to be conveniently mounted.
That's because you will need to buy an AUX adapter. Some cars will have an AUX button on the head unit but no AUX input.
The AUX input is usually located in the center compartment. If it's not, you will need an AUX adapter. You will have to install it yourself.
An FM transmitter is a second option. I would NOT recommend them as they are very cheap and low quality.
Getting an aftermarket head unit with an AUX input is a third option. I would highly recommend it.
Because that was an option. the head unit is the same, they have the capability to receive an auxiliary input, but the actual aux input unit was optional and yours did not have one, but that means you have an option to add one.
Hi this technology did not come until 2012 on most cars as we never needed it.