Interior trim falls under 2 major catagories, each is treated differently.
You have flexible, plush vinyl (seat covers, door panels). Vinyl GETS DYED.
And you have almost everything else – either “plastic” or steel. These get painted with interior lacquer paint.

ABSOLUTELY FOLLOW THE DIRECTIONS FOR THE PAINT PRODUCTS YOU’RE USING.

The parts your painting must BE ABSOLUTELY CLEAN. Otherwise the paint won’t stick to it. This means you need to remove dirt, dust, FINGERPRINTS…. I use SEM soap part # F3936 and a scrub pad part # S3.

Then the part is cleaned with a degreaser or paint prep. This eliminates any traces of mold release residue or fingerprints.  For plastic you’d use part # A3835 and for vinyl you’d use part # A3834.

Next, you coat the piece with an “adhesion promoter”. “Plastic” can use 2 different types. Flexible bonding adhesion promoter part # A3986, or “sand-free” adhesion promoter part # P102. Since you can’t sand vinyl trim (without ruining it), you use the sand-free stuff. This will allow the paint to penetrate the panel and stick to it.  I find almost everything that isn’t extremely flexible uses the sand-free agent.

Lastly, you put the top coat on. The 1st coat is normally applied when the adhesion promoter is still wet. You put several LIGHT COATS of paint on. Putting a heavy coat of paint will cause it to run or sag and peel off.

Vinyl seat covers and the like can be top-coated with a tack-free top coat to eliminate the “tacky” or sticky feeling after the part has been dyed.  This product is part # Q3964 and must be sprayed out of a paint gun.