qucik sanding question

[12Pack]

I just bought a car were the prev owner sprayed it orange over the org red. I want to respray it to org color. I know all I have to do is sand it down(not to bare metal) and shoot the color but not sure what grit sandpaper to use? I was thinking 320 should do it?

[ibidu1]

Its really hard to tell with out actually seeing the car infront of me. 320 if the paint is rough then pass over 600. Youll want the final to be 600 grit