Remove the radio. Check Youtube for removal. https://www.youtube.com/watch?v=gFvHl-MR6Io

Remove the metal covers. They are clipped on so just need to pry a bit with screwdriver.

Find the vias in the picture to solder your LEFT and RIGHT (Green / YELLOW) Audio Jack connector wires to and ground wire ( White) . 

Then burn a blank CD. I burnt an audio  CD with a 6 second silent audio track recorded with Windows Sound Recorder and thumb over mic input.

Some players do not switch to headphones mode when you plug in the audio jack so I needed to turn off car first.

So.

1. Insert the Blank CD

2. Turn OFF the CAR

3. Plug in your PLAYER ( If Car is ON my PHONE does not change to headphones )

4. Start CAR and Play away

Also: You could also drill a hole in the front plastic and put in a jack like this https://www.digikey.ca/product-detail/en/schurter-inc/4832.2300/486-3419-ND/1731055.  Then use a 3.5mm audio cable.