PPG makes a hard plastic parts primer:

It's a yellowish clear and somewhat viscous. It actually softens up the
plastic, to accept the solvents from the paints you are going to apply.

If I may suggestion, 3-M makes a great lacquer based plastic parts primer,
but the hands down winner is a two component epoxy primer. PPG makes it in
many colors. Apply the primer, then spray the paint.

Plastic parts do not accept dyes well at all, only softer parts, like
dashboard crash pads, soft vinyl door panels and seat vinyl accept vinyl
dyes. But certain brands suck!

Marhyde is a great brand, but there isn't availability to a mixing system
anymore, only pre mixed cans of color. So, next in line is SEM Vinyl Dye,
then PPG an last but not least is NAPA's Martin Senour Vinyl dye.

All are good products, but have worked well for me in the order listed. use
PPG DX440 as a wash/pre cleaner, because it is more aggressive than the
DX330. you'll need to use the mechanic gloves made of blue nitrile rubber,
because latex will melt as you use them.All chemicals work through the pores
of the skin, and you don't want to learn the hard way what the cans have
told you the medical consequenses have been, for years!

I hope this helps?

Refinish King

You must not be prepping it well enough or the plastic is too sun baked
and should be replaced.

The interior on my '71 T/A is vinyl dyed and has held up well for close
to 20,000 miles in the last four years.

Success! Thanks to all that replied.  This is the procedure that I
used.
1) cleaned all parts with TSP (tri sodium phosphate)
2) cleaned all parts with soap and water, then rinsed.
3) on the vinyl parts I used PPG's "vinyl cleaner an prep" SX1003
and on the plastic PPG's "plastic adhesion promoter" SXA1050
(apparently the key thing to remember with these products is to wipe
the parts in one direction only, to avoid seeing streak marks I
assume).  Then rinsed parts again, and allow to dry thoroughly.
4) using an air spray gun applied PPG's "elastomeric color" dye.

The dye was mixed up by my PPG dealer, I just gave him my interior
color code from the firewall tag.  I gave everything a couple of days
to set, then gave it the fingernail test.  I cant scratch this stuff
off!
Previous to this I did try Krylons fusion, and marhyde products as
some suggested.  But in my case they did not work.

Thanks again.