Newbie Question: burning through primer

[RoadRunner1083]

I have primered the body of the car and while sanding to smooth everything out, I had some white of the body start to show through the primer. Do I primer the whole thing again? or do I just spray primer in the spots that are now showing white? I tried to search this but didn't find what I was looking for. Pictures below show what I am talking about.

[martinfan5]

Prime again . what grit of sand paper are you using?

[RoadRunner1083]

400, should I start at 600?

[stulee11]

IMO i use 1000 grit to do my wet sanding on the primer, i know others on here have there own opinions and grits of paper they use .

[Mike Kucaba]

Are you blocking out or sanding with your fingers? Whatever you may be hitting a high spot,or the paper is conforming to your fingers. Make sure you soak the paper or cloth for a few minutes to soften the backing,and have something flat backing up the sanding medium.