Painting Brass

[Seamus O'Leary]

Unless it's very old brass or you've stripped it, most brass nowadays has been painted with brass-coloured paint.  If you're not doing any modifications, such as adding detail parts that are not brass, and therefore a different colour, a thorough wash with dish detergent, followed by a good rinse should be sufficient. 
You could still use primer, of course, and I would suggest it if you add such detail parts, but the brass coloured paint itself can act as a primer.

Wayne

And what detail parts would those be that one would add to bumper posts?