So I have a 2003 bmw 325 with the factory stereo and no usb connection in the car so there’s no way to hook up an external MP3 player. On the back of the stereo there is a port for the factory external cd changer if the car came with that option. My car did not, but it still has the port on the back of the stereo. A lot of people who have those cars take a 3.5mm audio cable and cut it so that they can hook up the wires to the corresponding leads in cd changer port and then plug it into a phone or iPod or whatever. That’s what I did, but as far as seeking forward and reverse I still have to control everything from my phone.

I’ve had other cars that didn’t have Bluetooth, but did have a USB port and when I used it to play music from my phone I could seek songs forward and backwards with the same controls on my stereo that would normally be used to skip stations or skip songs on a cd. My phone doesn’t have a audio jack, so I have to use a 3.5mm to usb c adapter into the 3.5mm cable which is wired into the back of my stereo.

So here’s my question, which wires in a usb cable would be used to seek forward and backwards? Are there certain colors that are universal for every usb cable? If I could find the wires then I’m guessing I should be able to hook them up to the appropriate terminals in the cd changer port since I’d be able to seek different songs on a cd using the forward and backward seek buttons on my stereo and steering wheel.

 

You need to send packets of data over the USB. It is not just a fwd/rev control.
So I think your project is doomed, unless you can add a computer to the car, and find the data format required, then write the code to make it all work.