Why does cheap brass plated hardware corrode so much?

[leadbelly]

You know what I mean, the cheap brass plated carriage lights and mailboxes that corrode like crazy outdoors.

Since they corrode very quickly even insalled in sheltered locations, my guess would be that it's galvanic corrosion between the brass plating and the dissimilar base metal.

Is it worth my trouble to put a protective clear coat on a new light I purchased or just accept the short lifespan?

[dmfraser]

If you live in a place with harsh winters, like Alberta, don't buy the cheap stuff. There is a reason its cheap. The plating on this cheap stuff is about a 1 molecule thick over untreated cold rolled steel. The plating might as well not be there when it comes to rust. Coating it will just make it look crappy and the hot summer sun will kill most any clear coat as very little of it has decent UV resistance.

I lived in Edmonton for 20 years and this cheap stuff just dies. If you want it to last, buy quality or decide you want a solid colour done with epoxy powder coat.