Ford F-150 Owner Teaches Us All to Buy a New Alternator

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Ford Alternators

Owner of a Ford F-150 with electrical issues keeps buying junkyard alternators and he keeps having problem. is the leading resource for information on how F-Series pickups, but the knowledge of the members can only be of help if you are willing to take their advice. This thread from the 1997-2003 F-150 section by “bbsitum” shows that if you have a problem and you ignore the information provided by the forum, your problem is likely to continue.

This thread should also remind us all that when we have a charging issue, we should always buy an alternator from a parts store rather than buying a cheap unit from a junkyard, as when you replacing things with junk parts, you never know if you’re making the situation better or worse.

The Introduction

When the OP first posed his question to the forum, he provided the following information on his truck, but he didn’t state exactly what he drives. His profile says that he has a 1999 F-250, but he posted the question in the F-150 section. Fortunately, an alternator question like this one is relatively universal from one truck to the next.

Replaced alternator with used one 3 years go. Sometime when is cold battery light would turn on for minute or so and would disappear. But battery voltage gauge would stay steady. Past Friday after driving for 50 miles battery gauge evidently start falling down and till I come home it was just above red and evidently pickup was sluggish. Battery light was on. When I come home I recharged battery that was empty as it get 7 hours to do it.

Battery gauge is one in upper right corner in picture. Since than alternator sometime charge sometime not. When is battery light on alternator do not charge at all as I checked with voltmeter. When is battery light off alternator do charge but voltage is not steady than change like 20 times per second and go from like 13,5 to 14,7 volts. I did voltage drop test at both side of battery to alternator connections and voltage drop is 0,02V at both side, that is 10 times below limit. Serpentine belt is old but do its job. Should I replace alternator as it work most of time?

Mind you, this same member posted about electrical issues five years back and it seems that he fixed the problem by installing a new-to-him alternator. Now that the problems have returned, he is questioning whether it is the same thing or something else.

Ford Gauges

The Community Responds in Unison

Pretty much everyone who replied to the OP to buy a new alternator from a parts store rather than buying a used unit from a junkyard. After all, when you buy a used alternator that has been sitting under the hood of a wrecked car for years, you have no way of know whether it worked correctly to begin with or how long it was on that vehicle. As you might expect, the community was quick to point this all out.

Bluegrass 7” was the first to point out the error of buying a used alternator.

How long do you think your going on a used alternator to begin with?
Time to replace it with a new or rebuilt and have the hassle over with.
The charge light comes on when the alternator has no output.
That is one of the functions of the regulator to indicate that.
Unless your going to tear the alternator apart and/or replace the brushes, it’s time to replace it.
Would be better off with another used alternator to go again and have trouble later again.
Old saying…..if you do what you always do, you get what you always got. Moral of this line is don’t do the same all over again and get the same result again.
Good luck.

The next member to chime in was “mudbug85603”:

Well if you insist on buying used junk then it might be a wise idea to buy two or three and carry the tools needed to swap it out on the road.

Or maybe you’d be better off joining an Emergency road service

He would later add this:

Just think of the time and money you wasted screwing around with junk yard parts. Junk yards are ok for somethings like body and interior parts but alternators, water pumps and so many other things it’s just smarter and in the long run cheaper to buy the good parts the first time. Now if you have one of those junkyard alternators laying around you can take that to a shop and have it rebuilt cheaper than you can buy one at the parts house. One more piece of advice….. Don’t buy the cheapest parts at the parts house either….. that’s a crap shoot just like buying at a junk yard.

However, the OP still purchased a used alternator from a junkyard for $20 and installed it, pointing out that it was working well.

“New” one from U-pull is already in and work good. Otherwise I agree, will not rebuild old one and would buy from store next time. How you go through so many ford pickup. I have same one from 2008.

More Problems

While the newest used alternator worked well at first, less than a month later, the OP was back, posting about charging issues.

Well 3/1/19 tm 8 days after everything worked good I was driving home from work and big snow was falling. And battery light turned on again, and was on and off in 1 and 1/2 hour that I did drive home. However battery gauge didn’t move. When come home with battery light on checked voltage and it was perfect 14,7 V steady. Two days after it when I drive from and to work battery light didn’t turn on. Weather was dry but cold. Today we had rain day and battery light come on and off (mostly on than of) again, same did yesterday even yesterday was dry weather. Checked multiple time charging voltage and all time was good and steady. So will just keep this alternator on till brake, if will do it, and will carry voltmeter around in pickup. Many people blame green wire at 3-wires connector at alternator to be not good. Will probably check it one day to. Possible will pull out alternator one day to check brushes etc.

“Broken wire coming off the alternator. It may not look broken but it could be broke inside the insulation. That was the story with my 4.6L. The battery light would come on and off, wiggled the single grey wire and it would turn the light on and off.” —— It is some of comments.

This struggles with alternators make me a better person. More interested in electricity and not freaking out when see battery light on.

At which point Bluegrass 7 offered a long list of information, but rather than listing it here, we suggest that you read his final reply in the original thread.

Meanwhile, until the OP gets away from buying junkyard alternators, he is likely to continue having charging problems that he cannot diagnose in his Ford truck.


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