1995 Ford F-150 • 185,000 miles

My alternator stopped working, so I got another one for free with wrong bolt holes and rigged it in and it worked fine. Then I got the proper alternator, installed it on the road and on the way home it worked at first but I watched my voltage decreasing all the way home. The next day, I checked it and it was working but then it stopped working again. I put a test light from the negative post to the negative clamp and the light went on which means there is a short. Then I took off the wiring harness from the alt and the light did not go out. I pulled each fuse one by one but the light never went out. What does this mean? Is the alt bad or is it a short preventing the battery from charging?
November 25, 2012.

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