Ford Alternator question

Tony Shelton

Tony Shelton

BS Detector, Esquire
Got a 96 F250 Gas 5.8l.

Occasionally the battery light will come on and the gauge will show that the battery is not being charged.

Last night we barely made it home as the lights got dimmer and dimmer.

One time it actually died and I had to charge up just to get home.

It only does this once in a blue moon. After last night it might go perfect for another month before it does it again.

I replaced the alternator about 3 months ago for this exact problem and the problem hasn't changed at all.

Any gurus know what I should try next?
 
I would check the pigtail on alternator To start.


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Use a meter and measure the battery voltage while the engine is off and again while it is running. You should have 12.6 volts off and around 13.8-14.5 running.

If you're still getting basic battery voltage while running, check both the 175A megafuse under the shroud at the firewall and also the 20A inline minifuse in the harness between the alternator and teh megafuse.


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I had a similar problem with a car many years ago.

At the battery shop they tested everything and found nothing wrong then it started doing something strange. I believe they changed out a diode or rectifier or something like that but the alternator was good. I think they said that the system was discharging or something like that.
 
I believe the diode and regulator are built in on that model which means replacement did not resolve the problem. Ford had a problem with the pigtails, one clue is if your new alternator comes with a new pigtail. This is an intermittent problem and is difficult to pinpoint unless you are able to recreate it and detect the problem when it occurs. Check your battery cables, you may want to replace the terminals ends. Check if you have a good ground from the battery to the ALT. Look for corrosion build-up or melted insulation near connections, fuse boxes etc.

Something could be shorting it out. Like a major accessory or bad battery. Some batteries will have intermittent short or low on electrolyte. If low on electrolyte the battery may not have much life left in it. Check the date code (little round sticker on the side of battery), the alpha will be the month and the numeral will indicate the year. Batteries pretty much go out when the date runs out give or take a year.
 
The battery is about a year old and the alternator is about two months or so old. I took battery connectors apart and cut back the one that had some space left and cleaned up the other one. I checked the pigtail and cleaned it up. It looked ok already.

I'll have to wait till it does it again and fiddle with the pigtail and see if that makes a difference.
 
I may have figured out what is wrong.

I think the alternator I got from Autozone has always been bad and the hotwater unit has been the source of charge for the battery this whole time.

I get no charge from the alternator and around 13 volts at the battery when the hot water unit is running.

Thinking back, the times when the light comes on and the battery goes really low are when we don't use the hot water unit for a few days and work off the cold water direct drive unit.

Looks like I need a new alternator.

Is it detrimental to the alternator to be putting charge back in via the hot water unit?
 
Back in Highschool I had several mustangs, mustang gt's and some friends had mustangs and we all would modify them as much as we could afford.

I stopped using autozone for all electrical parts and batteries. In 1 year I went through 14 solenoids. I bought an expensive solenoid from a different supplier and never changed the solenoid again. The next year I went through 4 alternators. Went to the expensive supplier and never had an alternator go bad again. The next year I went through 5 batteries. Finally learned the lesson and bought an expensive brand and did not have a battery go bad again. About that time friends were telling me that they had similar experiences with the electrical parts from autozone so I stopped buying the electrical stuff there and stayed with O-Reilly's or the dealer.

It was aggravating to say the least changing out stuff every month or two and at that point I started saving receipts in boxes because I had to have the receipt to change out the alternator, solenoid or battery.

I think they were getting all their electrical stuff from china, maybe one of the first to do so and it showed.
 
Tony Shelton said:
I may have figured out what is wrong.

I think the alternator I got from Autozone has always been bad and the hotwater unit has been the source of charge for the battery this whole time.

I get no charge from the alternator and around 13 volts at the battery when the hot water unit is running.

Thinking back, the times when the light comes on and the battery goes really low are when we don't use the hot water unit for a few days and work off the cold water direct drive unit.

Looks like I need a new alternator.

Is it detrimental to the alternator to be putting charge back in via the hot water unit?
Click to expand...

You need a blocking diode between the pressure washer and the battery.
 
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