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Discussion Starter #1
2001 7.3 F250
Had batteries tested and they checked out fine (per Oreillys)
My multimeter reads 13.5v on both batteries with the truck off, 12.5v on.

Replaced the alternator, still same results.

What else can I check to get this stupid light off???
 

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Same deal here. Guy I bought the truck from said the light has been on every since he replaced the alternator and both batteries. I am showing 14.25 volts while running and just over 12 off. Shows no codes.
 

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2001 7.3 F250
My multimeter reads 13.5v on both batteries with the truck off, 12.5v on.
That can't be though.... A static 6 cell 12v battery (like we all have) shouldn't be capable of producing 13.5v... If you're seeing 13.5 with the engine running and 12.5 OFF, that makes sense and actually shows the alternator is doing something...

Are you having any other problems with the system? (Flickering lights, dead/low batteries, etc.)

If you're sure the batteries are OK, and you've changed the alt already, I'd be giving All the connections and related wiring a real good look next (especially the alt plug) for signs of corrosion.
 

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Discussion Starter #5
FOUND IT!

I had checked Fuse #6 under the hood which was suppose to be for the alternator and it was fine, but I never checked #7 (secondary alternator) because my truck isnt equipped with the secondary alternator. However I pulled #7 today (5 amp) and it was blown. Replaced it and the light went out. I have to get taking off to work now, but I will bust out the multitester and test everything after. But yes, the batteries read 13.5 off, and 12.5 on. This also had me confused.
 

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When you are testing it with the engine running, are the glow plugs still on? If so that is probably why the reading was so low, they draw a lot.
 

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When you are testing it with the engine running, are the glow plugs still on? If so that is probably why the reading was so low, they draw a lot.
Actually, the way the system works is the PCM switches the alt OFF during the times the GPs are On. So, for the first min or two you won't see anything over batt voltage so the alt is being saved from being overloaded trying to recharge the freshly cranked-down batteries AND the load of the GPs (over 150A)
 

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Good catch! I had mine on too. Ended up being a funky thing with GEM modual. Made a few things wack.
 

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Actually, the way the system works is the PCM switches the alt OFF during the times the GPs are On. So, for the first min or two you won't see anything over batt voltage so the alt is being saved from being overloaded trying to recharge the freshly cranked-down batteries AND the load of the GPs (over 150A)
I'm having the same issue...
I hear it might be the yellow or red wires but I ohmed them out under front of the motor (where Ford said they were bad at) but they read less than .5 What else should I do??? I need help!!!
 

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YOUR BATTERY LIGHT IS ON.....DOES YOUR TRUCK TURN OVER?....

DOES YOUR TRUCK START?....

DOES YOUR TRUCK RUN NORMALLY?....

IF IT DOES ALL OF THE ABOVE.....AND YOUR BATTERY LIGHT IS ON.....YOUR ALTERNATOR MAY BE GETTING WEAK OR GOING BAD.....

YOU MAY WANT TO HAVE IT TESTED.....
 
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YOUR BATTERY LIGHT IS ON.....DOES YOUR TRUCK TURN OVER?....

DOES YOUR TRUCK START?....

DOES YOUR TRUCK RUN NORMALLY?....

IF IT DOES ALL OF THE ABOVE.....AND YOUR BATTERY LIGHT IS ON.....YOUR ALTERNATOR MAY BE GETTING WEAK OR GOING BAD.....

YOU MAY WANT TO HAVE IT TESTED.....
It does ALL of the above (sorry about not including all of the above)... I actually just got from under the hood comparing the alternators. The passenger side alternator has a layer of dark colored copper coils and the rest are clean... The other alternator looks great.
 

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following... I have the same issue, New batteries, new alternator, new 2 wire pigtail, and fuses are good. battery light in dash stays on. I have hooked up mutimeter to all electrical components individual and there reading are within spec. battery light came on when my original alt. was failing and it has been on since changing all issues.
 

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On another vehicle found an area in the Positive wire where it was burnt and started to melt was causing the battery light to go off.

I’d probably Next clean grounds, including frame grounds and battery cables.

Next would be pull the batteries and alternator and take to a parts store to test. If the light is on all the time and it’s those, they should test bad.

Any mods drawing power like compressor that may not be fused right?
 
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