[Dave F]

Please do not laugh too hard if I am way off base here. I have a 75 TA and I have the grills out of the front and I am trying to fix them up due to some overspray from a previous paint job. I am not looking for show quality, but I do want them to look nice. I taped the areas that I did not want to get paint on and proceded to paint the areas that needed it with some enamal spray paint. Even though I used a "plastic primer", the paint will not stick in some places. It starts to bubble and looks like the desert floor during the middle of summer. Is this the wrong kind of paint? Do I need to do something else to prep the plastic? Will spray paint work or do I need to take these to a body shop to have them painted? Any advice will be greatly appreciated.
Thanks,
Dave F