This past Wednesday night, the alternator light in my '87 Ford Ranger came on. Thursday morning, I went by an Auto Zone store to have them test the alternator while it was still on the truck. The "technician" said that it was bad but that to be on the safe side of being sure, I needed to take the alternator off the engine and bring it back in to be tested off the engine.
Well, Thursday evening I took the alternator off the engine. It is one of the simplest truck repairs I've ever done. Remove two bolts, unplug two wires, and it's off the engine. I took it back to the same Auto Zone store that I went to in the morning.
A different "technician" helped me this time. The first test that he ran came back saying that it was bad. However, he ran the test again and this time the alternator came back okay. The "technician" said that it could be something else, like the wires running from the alternator to the battery, but he wasn't sure. I could either buy a replacement alternator or try to figure out what the problem was.
I didn't want to spend the money if I didn't have to so I decided to take my chances and put the old alternator back while I tried to figure out what the problem was. However, on my way home, there was something that told me that the alternator was in fact the problem.
Instead of heading home, I went to an Advanced Auto store that I normally go to. I wanted a "second" opinion on my alternator. Sure enough, they ran two tests on the alternator and both came back as faulty. I purchased a new alternator from them, went home put it on the engine, crancked the engine and to my pleasant suprise, the alternator light was no longer on.