I have a 1993 F-150 5.0. It was running fine earlier this year, but I had to stop driving it for several months. When I tried to start it, the battery was dead, so I recharged it and it started just fine. A few blocks down the road I noticed that the voltage had dropped, so I came back home and swapped batteries, and it was still dropping. I checked the output from the alternator and it came back at 12.4 which is the same as the battery so I figured that the alternator was probably the cause. So I replaced the alternator and went to hook the battery back up, but my other battery has the terminals in the opposite position and I forgot to reverse the position when I put the original battery back in. It sparked at the battery pretty violently and that's when I knew I had done something bad. I quickly flipped the battery around and tried it again, and it started right up. However, the alternator is still not charging. I took the alternator to a local guy who told me that it was probably the regulator on the alternator and swapped it for a new one, but it still doesn't work. So I pulled the wiring from the starter solenoid to the alternator and checked it for any damage and it was fine with strong connections on all ends. So now I'm wondering if there was something else in the alternator that might have fried due to the battery being put in wrong. I've checked all of the fuses in the interior and in the engine fuse panel and they are fine. I didn't see any fusible links in the wiring from the starter to the alternator. Everything else works just fine and the truck is driveable for short distances (until the battery dies).

Any advice before I drop money on yet another alternator?

 

Take your current alternator to your local parts house and have them test it. Here they test them for free. Heck, any more I have them test the new ones before I buy them.

 

I didn't even think about doing that. There is an Autozone right by me that advertises free testing of parts. I don't know how true this is, but I've heard that a lot of alternators come brand new and DOA.

Thanks!