good v. bad
FTE Legend
Joined: Jul 2010
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From: Northeast, OK
There are differences in brands, but that doesn't always translate to differences in price as some places have them at better prices than others. I think Motorcraft is the best, but I'm not sure they aren't made in China any more. I bought
a couple of years ago from Amazon and it is working well.
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Freshman User
Joined: Aug 2014
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Got a Motorcraft GR540B regulator . put it in today . With the voltmeter connected to the battery , I have 14.6 v at idle ' between 15.3 and 15 .55 v with the headlights on in fourth gear . I'll see if it discharges in the morning .
FTE Legend
Joined: Jul 2010
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From: Northeast, OK
You still have a problem. The 14.6 is good, but it shouldn't go any higher than that. And, 15+ will boil your battery dry and cause the various lights in the truck to burn out quickly. Have you checked the diodes?
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I am going to remove the alternator today and check the diode tree after work today . I have the info on how to check , but I can't remember what I need to do . I will need to do my homework .
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FTE Legend
Joined: Jul 2010
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From: Northeast, OK
I wouldn't have started the engine without checking the diodes as you could fry your new regulator.
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FTE Legend
Joined: Jul 2010
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From: Northeast, OK
Sounds like you have a bad diode. But are you using the diode check setting on a meter as that should show a low #, like the 1, in one direction and infinity in the other. And I think 535 is too low. But, tomorrow I can test a couple of my known-good alternators to see what readings I get.
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The diode checker feature on the meter checks the forward voltage drop on the diode. Depending on the diode you will get around .7v in the forward or "conducting" direction. You will get a very high reading in the reverse direction.
FTE Legend
Joined: Jul 2010
Posts: 32,875
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From: Northeast, OK
Are you using a diode-check function or just the resistance scale? If you have the diode function you should use it. But, in any case 563 ohms is not close to infinity, so I think you have at least one bad diode.
Another approach is to check the AC voltage with the engine running. Google "alternator diode check" and you'll find some videos on checking the AC voltage. But your testing so far tells me you have a bad diode.
Another approach is to check the AC voltage with the engine running. Google "alternator diode check" and you'll find some videos on checking the AC voltage. But your testing so far tells me you have a bad diode.
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