Blinking battery light

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May 13, 2015 | 10:01 AM

andym

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From: Bonita Springs FL

Blinking battery light

The battery light blinks in my truck. It's not a controlled blink, but it flickers like a loose bulb. It started a week or so ago. It would blip every once in a while. Gradually it would start to flicker more often. At first I thought it was belt-related but it isn't related to the transmission shifting at all. So if you're thinking that it's belt-related, you're going to have to explain why it doesn't blink either right before or right after a transmission shift (i.e. a rapid change in engine speed).

Earlier in the week, the light was flickering so hard that it was virtually on. I drove home last night and didn't see it once, although that's the first time I haven't seen it happen at all in a week.

The battery gauge itself doesn't move a bit while this is happening. I have a cigarette lighter voltmeter and it shows a pretty steady 14.1 volts regardless of whether the light is flickering or not.

I had the batteries tested in my truck by a real battery shop about 4 months ago and they are fine. The battery connections all seem tight and clean, and the belt, tensioner and all that seems fine.

So... ideas? What can cause a battery light to come on that isn't voltage related?

May 13, 2015 | 10:08 AM

texastech_diesel

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Joined: Jun 2007

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From: Breckenridge, TX

What's battery voltage reading across the battery when the light flickers? Or between the alt case and ground?

I'm trying to think where the PCM reads voltage from, and where a drop could be that's not showing up elsewhere except through the PCM. Wiring connectors somewhere is my guess.

May 13, 2015 | 10:12 AM

andym

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From: Bonita Springs FL

Quote:

Originally Posted by texastech_diesel

What's battery voltage reading across the battery when the light flickers?

I included that information in the OP. 14.1 volts regardless of whether the light is flickering or not.

Quote:

Or between the alt case and ground?

Isn't the case bolted to the engine and therefore grounded?

May 13, 2015 | 12:30 PM

texastech_diesel

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From: Breckenridge, TX

Sorry, not case but alt stud and ground, ie voltage at the alt itself. And the again what's voltage not through the cigarette lighter, but across the battery itself.

Then what are the voltage drops between alt stud and battery positives, and between other places like PCM power supply and alt, or if the dash cluster is fed through a separate circuit from the PCM (ECM on 7.3?) and body power, from those connectors to the alt stud.

You have to figure out if voltage is dropping across one part of the circuit but not across another part. Just because the cigarette lighter reads 14.1 doesn't mean the entire system is the same, that's one part of it. The battery light might feed directly from the engine, or it might go through the PCM, IDK on a 7.3.

If someone has a 7.3L wiring diagram, you can figure out what feeds the lamp, what feeds the PCM, and what feeds the cigarette lighter and isolate. If the lamp is fed separate of the PCM, then there's probably a connector or wire in that circuit that's causing a voltage drop you aren't picking up though the cigarette lighter.

May 13, 2015 | 02:04 PM

DavidB

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There are several things that "could" cause your symptoms, but the most common is worn brushes in the alternator. If that is the problem, eventually the light will just stay on all the time, in the meantime you may experience low battery problems. Just because you read 14.1 volts across the battery terminals does not necessarily mean that all is well with the alternator. Of course, you could also have an intermittent bad connection somewhere.

May 13, 2015 | 08:03 PM

dkf

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Joined: Mar 2007

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From: Pa

Mine would come on intermittently above 4k rpm. When I tore the alternator down to rebuild it, why the light came on was obvious. One of the brushes was severely worn.

A 7.3l should have two 6G small case alternators which are a little more involved than the 3G to pull the voltage regulator to check the brushes but it is still not difficult. Possibly one alternator is dropping voltage causing the light but the other alternator is still good and keeping the voltage from dropping.