Wet sanding, final grit?
 

Ok, sanding down a car, miata, bumper covers and fender. Will be painted while off the car. I am not sanding to metal or bare plastic. When wet sanding and preparing to do the final sand what grit of sand paper should I use to best prefare the surface to hold the paint the best. Assuming everything to this final point was done correctly what final grit should I finish with. I am not sanding to bare surfaces so I was not planning on priming since the orig paint is still there just sanding down.

if your doing a scuff and shoot, then your last step would be done with 600 grit. 600 after 320 works great on primer, but for paint that is in fair condition i use red scotchbrite pads. scuff it dry, or with a 3M scuffing agent available at most paint shops. good luck and post some pics.

Id go for 1000 or 1200 grit paper

depending wether or not is a solid colour or c.o.b you can use 800wet and dry if its solid I just use 400 or 320 wet and dry

For a great finish ( dependent on your spraying skills ) when you have completed wet sand with 650 , a final 10 mins with very wet 1000 ,should be fine . Dont go too mad with 1000 , as you do need good adhersion to you substrate.

1000 wet is fine to finish with but 800 will be fine that's all I use on cob paint everyday as im a painter specialising in resto work

scratches from 320 wont show threw paint. i would use 320-400 to skuff for a repaint, it will give the new paint a lot of tooth original paint as long as its not peeling or flaking makes for great primer so try not to go threw the paint to the metal. and you wont need to apply a primer.