Depends on what is bad on it. The brushes on one were wore down, so I replaced them. I took the alternator out, and took everything that can easily be removed off. I them sprayed brake cleaner all over it, getting the dried dirt and grit off. The. I took an air hose and sprayed everywhere I could.
I bought new brushes at O'Reillys ( weird they're called brushes when they're just little metals rods) and soldered those on. Another good wipe down and reinstalled. Took about 3 hours and $8, and I was good to go.
If it's another part that's bad, you can buy replace tons for them as well. I knew it was my brushes from their condition so I went with them first.
How to Rebuild an Alternator: 29 Steps (with Pictures) - wikiHow
http://forums.mightycarmods.com/show...-(On-the-cheap!)
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