Re: 2003 Focus SVT with Alternator Failure
The terminals at the battery flat suck. They can be super tight with a wrench and still be loose enough to pull off by hand and especially if the battery posts have been cleaned to remove some slight amount of material.
Make sure the replacement alt is a Ford official Motorcraft one and even possibly an error there. Many dealerships here use the commonly available 'lifetime warranty' OTC part at the local parts stores, they then overcharge for the work while letting you think the parts are official Ford ones. The Chinese rebuilt alts now used are utter garbage and very common to fail as many as 2-3 or more and quick now, they use substandard parts since they know the warranty will have them replacing the alt every time they turn around. I know because I had to pretest every alt sold, and MANY failed right out of the box. One of the most serious part issues out there now.
The harness to alt can be bad as well, there is a replacement pigtail to fix that.