Technical Painting parts over primer

The bed sides of my pickup bed were painted with 2 K primer 8 months ago.If I sand them with 180 sandpaper can I paint them with Blk. urethane or should I respray a light coat of primer on them first.Thanks

 

Sand them with 400 and paint. 180 will leave lots of scratches in your final paint.

 

I go to 400 wet prior to top coat.

 

Thanks for the replies.