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2005 F250 6.0, 215K miles, owned since new all maintenance preformed mostly on time and all the things that can go wrong did! Currently on extended RV trip. Short side of issue, Batt light intermittent-truck running check with multimeter- light on or off-13.8 volts at batteries. Later Batt light on more than off, checked batteries-12.0 volts after long drive time. AutoZone-test-batteries good-low-need to charge before test alt. Charged overnight-test alt-internal regulator failed-New not rebuilt alt-installed-charged batteries-light on after GPs off- alt output 0. Test new alt at AutoZone-internal regulator failed same as old alt-batteries 90% & 100%. Test old alt 7 times all pass don’t think it the alt. Miles later batteries low-charge overnight-start-drive 10 miles-oil 140 degrees-no Batt light-test volts at batteries with multimeter truck running-14.3 volts- go to turn truck off-Batt light on-test again at batteries 12.5 volts. Ohm test between Alt red wire and battery-good. Engine on-warm-no output from alt-engine off-key on-no voltage on green wire. Did not test other alt wire. Checked fuse 45-good. Do not see issue with oil temp wire. If I understand correctly-engine cold-GPs on-no power to alt-after engine oil warm-GP off-power to alt at green wire. Is this correct? Is the voltage to alt controlled by the GPM? If so, which wire can I test out of the GPM to see if it is providing voltage to the alt. If not, where does green wire get its voltage? Any suggestions appreciated. Thank you!
 

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It's probably easier to give you the Ford service instructions and layout rather than bantering back and forth.

With the 110a alternator, it can seem like the alternator is held off, but it isn't. The current draw for the glow plugs, battery recharging, and engine electronics overwhelms the alternator's capacity, so the voltage is low. Once the glow plugs turn off, the alternator can handle it. I'll add the graph from a higher capacity 140a alternator, which was an option at the time of purchase so that you can see the difference. Many owners change to a 140a alternator with a small pulley to get more amps off idle.

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Rectangle Slope Font Parallel Pattern


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Schematic Slope Rectangle Font Parallel
 

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Discussion Starter · #4 ·
Thank you for the quick response, info, charts and reading material! It is greatly appreciated. Just so I am clear, are you saying there could be many items causing the issue and then get a 140 amp alt, or are you saying get a 140 amp alt and enjoy the rest of your trip? Sorry, sometimes I am not the brightest bulb on the tree.
Thank you again!
 

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Maybe I should have given you a link to my video. But, first, let me unpack what you wrote.

QUOTE

2005 F250 6.0, 215K miles, owned since new. All maintenance was performed mostly on time, and all the things that can go wrong did! Currently on an extended RV trip. The short side of the issue is the Batt light is intermittent.

Truck running, a check with a multimeter with the light on or off shows 13.8 volts at batteries.

Later, the Batt light was on more than off. Checked batteries-12.0 volts after long drive time.

There are two things the "battery" (Should have been a charging light) light is telling you when it is on.

  • The alternator is not charging (light off).
  • The alternator diodes are not in good condition and introducing AC into your system. You can have suitable voltage with bad diodes.

AutoZone tested the batteries, which measured good to low, so we needed to charge the batteries before testing the alternator. Charged overnight; test showed the internal alternator regulator failed.

The auto parts stores are not infallible and sometimes do not do a good job at all.

New, not rebuilt, alternator installed; charged batteries, but the light is on. After GPs are off, the alternator output is 0.

Test new alternator at AutoZone; internal regulator failed same as old alt. Batteries 90% & 100%.

Test old alternator seven times: All pass - I don’t think it is the alt.

Again, auto parts stores analysis can be questionable. And auto parts store alternators can be bad out of the box.

Miles later, batteries are low; charge batteries overnight.

Whatever alternator is on the truck ain't working.

Start driving 10 miles .... no Batt light. Test volts at batteries with multimeter truck running-14.3 volts. Working.

Go to turn the truck off; the Batt light is on. Not working.

Test again at batteries 12.5 volts. It should be around 13.5v if the alternator is working and the truck just turned off.

Ohm test between Alt red wire and battery-good.
Engine running and warm; no output from alt.
Engine off-key on; no voltage on green wire. Cluster/connector/wiring.
Did not test the other alternator wire. The other wire is the 'sense' wire; it then is the reference that tells the alternator how much to output.
Checked fuse 45; good.

I do not see an issue with the oil temp wire.

If I understand correctly, when the engine is cold and the GPs on, there is no power to the alternator. After the engine is warm, the GP power is off to alt at the green wire. The signaling Power to turn on the alternator is on anytime the key is on.

Is this correct? Is the voltage to alt controlled by the GPM? NO.

If so, which wire can I test out of the GPM to see if it provides voltage to the alternator?

If not, where does the green wire get its voltage? Per the diagram, the light green/red stripe wire is the grounding side of the 'battery/charging' lamp. When the key is turned on, positive goes through the fuse 45 to the cluster and then the one side of the 'battery/charging' lamp. The other side of the lamp is the light green/red stripe wire going to the alternator. When the alternator is not producing electricity, it acts as a ground for the lamp, so it's on. When the alternator is producing, there is an equal voltage on both sides of the light, so it does not glow; no ground.

Side Note - If a diode is bad, the voltage will not be rectified close to battery voltage; it can be up to -1 to +1, for example. So the voltage swings at the alternator are not equal to the voltage at the batteries (key switch), and the lamp can come on.


Any suggestions are appreciated. Thank you!

End QUOTE

While you might have a cluster issue, it's more likely you may have a connector issue at the alternator. If it is not fully engaged, or the wiring at or an inch or two away from the connector might be frayed, this can cause battery light fluctuations. There is a tab on the connector that should lock firmly into the alternator's body.

You can buy connectors with pigtails at the auto parts store to replace them if needed. I had to on mine. In the field, you would have to use the crimp-on butt connectors to spice it correctly, ensuring the wires go to the correct side of the connector. The replacements are not correctly color coded.

The one thing I'm worried about in your description is the voltage of the light green/red stripe wire only stayed on for a short time. That might be an issue with the cluster or an indication of the wires frayed. Note - I don't care for test lights; I don't own one. I use multimeters and check for voltage or continuity.

The Ford Service Procedures have a step-by-step process for checking all this.

You can use the 110a alternator, a 140a, or up to the 300's. Most prefer something at least in the 140a range, and both the 110a and 140a alternators perform better in this vehicle with a smaller pully to increase the idle speed output. But changing to a 140a or other alternators will not solve this unless you have the unfortunate situation of two bad alternators.

My video on the subject.

That Darn Battery Light
 
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Discussion Starter · #6 ·
Please do not respond as I have used enough of your time. I want to thank you for the detailed response and the video. Because of you response I have a better understanding of the charging system. The video is above and beyond excellent, full of information and proper procedures! I plan on changing the connector and properly retest. If it ends up being a cluster issue I will take the truck in for service because as you say, I am in the Field. Thank you again for the education, I will put it to good use.
 

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Not a problem, RVer, even with more questions. Glad to help.

If you are parked for some time (days), you could send the cluster to Circuit Board Medics - Automotive & Appliance Circuit Repair. They can do a quick turnaround and will test the cluster and send it back with a minimum charge if it's OK.
 
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Hi TooManyToys, hope all is well! I will take you up on your offer and ask another question before I make an appointment at a repair facility 100 miles away.

Test results: Unplugged old and new alternator connector, green/red stripe wire, hot or cold engine, tested at connector, 12+ volts. Either connector plugged into old or “New” (The one purchased a while ago) alternator, key on, 1.9-2.4 volts. Any suggestions?

Test procedures: I do have a temperature gauge on the truck and what I have noticed is when the engine is cold the Batt light does not luminate. Once the engine reaches operating temp a few minutes later the Batt light does come on. I have verified this many times.

There is a NAPA store 15 miles from here and I was able to secure a new connector. With the warm “New” alternator unbolted I did unplug the old connector and tested at the connector the green/red stripe wire with the key on. The battery was 12.29 volts and the connector had a consistent 12.24 volts. I plugged the connector back in and that voltage dropped to 1.9 volts. I removed the “New” alternator and connected the large red wire to the cold “Old” alternator, warm engine, key on, connector disconnected, 12.24 volts, plugged in connector, dropped to 2.5 volts.

“New” alternator installed, new connector (I did hear it click & insured correct wire connected to proper wire with butt connectors and shrink tube) installed and plugged in, disconnect glow plugs, key on, cold engine, checked voltage of green/red stripe. Rapid but continuous fluctuation between 1.9-2.4 volts.
The sense wire and the large red wire have a constant 12+ volts.
Thanks again for any help!
 

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This is a single alternator vehicle, correct?

Hopefully, you are checking voltages with the engine running by back-probing, not disconnecting connections, including the heavy cable connections.

All of your voltages check out. From the service manual, I gave earlier.

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With the connector on, back-probing the I circuit without the engine running should be in the 1-3 volt range. You are measuring the voltage between the alternator and the lamp; between two resistances.



Could you please take pictures of your battery and alternator connections?


Dual Alternator 6.0L reference.

Watch Hood Motor vehicle Automotive tire Electrical wiring
 
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