When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Unless the chrome one's a real mess,
find a plastic one to start with. It's going
to be a real pain to scuff all of it to get paint
to stick.
With plastic, you just clean it, hit it with 'plastic primer'
(I use SEM brand with success)
and then have at it. Around here, $25 in the junkyard
will save you a day with 400 grit sandpaper.
Chrome or the aluminum grill? If it's aluminum, sand it with 400 grit until there's no shiny spots, if you slack off on the sanding, it'll eventually peel. Clean it with acetone or MEK. Use rubber gloves and do it outside, especially with the MEK, it's n nasty stuff. The MEK will strip any surface corrosion off the aluminum. Use an etching primer specifically for aluminum, it's tricky to get paint to stick to aluminum, use the right products. Then you can top coat with whatever.
If it's real chrome, good luck scuffing it enough to get good adhesion. I used diamond emery cloth on some old chrome rims until they didn't shine anymore, and the paint still peeled within a year. Another option is to look into getting it powder coated. They'll usually sand blast it first.