Alternator question

Dieselwrench · Oct 27, 2015

What controls the alternator charging cycle? I've got an '05 that I can't tell if it's charging correctly. Right now I can only check the system with a multimeter while the truck is sitting still, but I don't think it's charging correctly. The most I've seen is 12.5 volts. This is with the headlights, interior lights, radio, and blower motor all turned on. Just for fun I replaced the alternator with a rebuilt one I had and hit the same results. I also had the local O'Reilly's check the alternator I took off and according to them it passed. I also checked the voltage on an '02 6.0 at work. The '02 showed 13 to 14 volts with the headlights and blower motor turned on. My '05 never has the battery light come on nor do I ever see the lights dim or have any indication that the charing system is not working. The batteries do sometimes require a trickle charger, but I think that's mostly due to lack of use. The truck is parked outside all the time here in Oklahoma and driven maybe two times weekly. Sorry for the long post and thank you for any and all information.

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Dieselwrench · Oct 29, 2015

Anyone got a wiring diagram from the alternator to the chassis on an '05 F250?

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DEEZUZ · Oct 29, 2015

Alternator doesn't kick on until after glow plugs are done. The only wiring I've ever messed with leads up to the fusible links by the battery.

Dieselwrench · Oct 29, 2015

I have been told that the two wire connection at the alternator has one wire hot all the time and the other is ignition powered. My alternator has one wire hot all the time and one dead. I am missing the ignition power to excite the field in the alternator. I need to find out where that wire is fed power from.

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Bustedknuckles · Oct 29, 2015

Dieselwrench said:
I have been told that the two wire connection at the alternator has one wire hot all the time and the other is ignition powered. My alternator has one wire hot all the time and one dead. I am missing the ignition power to excite the field in the alternator. I need to find out where that wire is fed power from.

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On a 03 it is fed from the instrument cluster. I assume a 05 is the same but cant say for sure.

Bustedknuckles · Oct 30, 2015

Thats a diagram off a 03, wouldn't be hard to figure out if it was the same on a 05.

Dieselwrench · Oct 30, 2015

^^^^ This is the plug at the back of the instrument cluster, correct?

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Dieselwrench · Nov 1, 2015

I HATE RATS!!

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pdumont01 · Nov 2, 2015

Nice find

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Snake · Nov 2, 2015

CTC DEEZUL said:
Alternator doesn't kick on until after glow plugs are done. The only wiring I've ever messed with leads up to the fusible links by the battery.

On single alternator trucks, its on with the glow plugs. The OEM unit just can't keep up.

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rodeo302 · Nov 22, 2015

Sorry to bump an old thread, but I don't see a point in starting a new one. I have a single alternator on my truck is it normal to be sitting around 12.5 volts in both batteries at idle

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Snake · Nov 22, 2015

rodeo302 said:
Sorry to bump an old thread, but I don't see a point in starting a new one. I have a single alternator on my truck is it normal to be sitting around 12.5 volts in both batteries at idle

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I'm afraid not.

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rodeo302 · Nov 22, 2015

Damn alright thanks, so I'm guessing alternator is most likely

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Snake · Nov 23, 2015

rodeo302 said:
Damn alright thanks, so I'm guessing alternator is most likely

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There's a good chance, but also have your batteries load tested.

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rodeo302 · Nov 23, 2015

Well one is new yesterday, and the other one was new earlier this year, so I'm guessing they are fine. Hopefully I can drive 20 minutes one way with it and still get home and fix it.

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black'n'blue · Nov 23, 2015

Check your cables. I have the same problem and put the larger 140 amp alternator on from the dual alternator setup that some of these trucks come with. It helped for a few weeks but I'm still around 13-13.5 volts. Cables will be next for me

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Extended Power · Nov 23, 2015

I'm looking at getting a DC 270XP or bigger alternator.
Right now I have a Team Green 200 amp, but I don't think it's enough to keep everything I have running, and charge up the batteries at the same time.
It's close, but I think they are slowly declining in voltage.

The other thing I haven't changed, is the first foot or so of the wire leaving the alternator, to the batteries.
It's still the stock wire...whatever small size it is.
I have run heavy cable from where the thin wire joins to the wire going to the batteries...I just didn't have the right connector at the time....and JUST remembered. :doh:

rodeo302 · Nov 24, 2015

The alternator failed everything so I replaced it and now it's amazing it starts way easier glow plugs are working properly again and everything thanks guys

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Snake · Nov 24, 2015

rodeo302 said:
The alternator failed everything so I replaced it and now it's amazing it starts way easier glow plugs are working properly again and everything thanks guys

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Awesome! Thanks for the update.

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