odd alternator problem
 

I know the alternator has been kicked around a lot on here already but I have a strange situation..my alternator went out so I got one from a yard in CT. it seemed good and even said remanufactured on a sticker, and it did work good for about 300 miles, then the warning lights came on. so I had about 30 miles to go , I turned off everything that I could such as the a/c, radio and even the lights as it wasn't near dark yet. well after about 9 miles the lights all went out so I figured it might have just been burshes not seated good but the next day after a few miles the lights came on again. This time I put the old alternator back on and it worked fine. I checked with a volt ohm meter with the ground lead on the neg. post and the the red lead to the positive post and it checked good ,, it did vary with speed of engine and accessories but was above 12.7 at the lowest and was up in the 14's at the highest. Well I though I would put the one back on that I got recently and stopped working just to check the voltage on it.. and it tested about the same but I drove it only about 4 miles and all the lights came on again so I came home and checked it.. it was still showing good voltage readings but the warning lights were still on. I put the old alternator back on . and it checked the same as the one that made the lights come on but with the old one installed the lights stay off... does anyone know why this is happening?? it is just curious to me??? thanks. Vernon

Any signs of belt slippage? How is the bearing in the tensioner pulley?

Yes the belt is plenty tight in fact it is only a couple of months old and I even changed the bearing in the idler not long before that.. what is odd is both alternators show good voltage when I check with a volt/ohm meter at the battery posts but one of them allows the warning lights go come on and the other doesn't. that is the odd thing about it and the one that does light up the warning lights is very clean and even had a remanufacture sticker on it, I think I will take it to an alternator guy near here and see if he can figure it out, the burshes even look new in it.. But then I guess there is something in there that isn't doing something right.. Thanks . Vernon

It could be that the solder connections are failing at the rectifier, making an intermittent circuit. This happens on a number of alternators, especially during the summer heat and high loads.