Audio Systems: Stereo removal, phillips screwdriver, ford radio

Question
I have an 89 Lincoln and cannot figure out how to get the stereo out of the dash. The face plate has a small hole at each corner and no obvious screws attaching the face plate or stereo to the dash. I have used a small phillips screwdriver to attempt to find a fastener in the holes but have found nothing other than there appears to be a spring load but the face plate does not release. Thank you for any help that you can provide.The car has a cassette player in with the stereo and a seperate factory cd player with the same type of face plate.  

Answer
you have to insert the tools all 4 at once, there's tools available from ford dealers and some auto parts stores, ford radio removal tools, nothing more than u-shaped coathangers with notches on the ends that you insert into the holes far enough for notches to engage in the catches so you can pull radio out. once you've even seen the tools, you can easily make them with a coathanger and a file to make the notches in the right places....