Primer Problem. Please Help!!!

[84C10EC]

I am restoring a set of Boss 338 wheels and have stripped and primed them with 3 coats of self etching primer. I am currently in the process if wet sanding the primer with 400 grit paper to prepare for the top coat. 400 grit was recommend by the manufacture of the primer. As I have been wet sanding some of the primer has been sanding off exposing some of the aluminum. Its been minimal and mainly just at sharp edges. Do I need to apply another few layers of primer? If so should I continue with self etching or should I use something else? Appreciate any help and advice. Thank you.