Battery light flickering while driving
 

Just hopped in my truck a few minutes ago. Started fine, batteries are strong. Started driving and got about a mile from the house when I noticed the battery light flickering as I'm driving. So I made a u-turn and came back home.

I noticed the light goes out completely at idle. Nothing. It only flickers while driving.

With the engine running I yanked out my multimeter real quick and checked the power at both battery terminals. Both showed 13.95 volts. Checked at the alternator, showed 14.12 volts at idle. Checked other constant power areas such as the hot side of the GPR and IAH relays, both registered 14.0 volts at idle.

I reformatted my hard drive not too long ago, and I haven't re-loaded AE yet. Guess I'll have to do that soon, that way I can hook up, monitor vehicle voltage, and drive around to see what my voltage looks like when the light is actually flickering.

All cables are fine. I've checked those again today, and I've completely inspected those recently. So there isn't a wiring issue. Looks like I have another alternator on the fritz. If I replace it, that will be #5.

Unless anyone else has other ideas I should check? I didn't expect to see such good voltage at idle. Every time my other alternators failed before, I could see voltage drop at idle.

first thing that i think of is a bad diode...go have her tested at a parts house (on the vehical) and see what they say. I drove around for over a year on a bad diode(ther are 3) and being a diesel it still was able to produce enough charge for truck oppeation (i dont have PW PL or any power acc). if there is a bad diode, its time for a new alt.

I just read you have already put in 4 alts, how old are the batteries?

How many volts do you have durring cranking?

How many volts at idel, all loads off? all loads on (hi beams, blower on hi, ect)

I would think if your bat volt sense wire was havving an issue you would see an overcharged battery condition like excessive volts and posibly low on water

Check the small plug that goes into the top of the alternator. Mine gave me fits last year with the same type of issue, I finally ty wrapped the harness to keep it from moving around and it has been fine ever since.

Batteries are a year and a half old, the gold top ones from Autozone.

I don't know the cranking volts. But the batteries are good. Starter spun just fine, fired right up as always. I don't suspect batteries at all right now. I will check them when I get a chance. Right now I'm in the middle of doing 10 things at once.

I quickly checked the plug, it was tight. Didn't actually pull it off to look for any corrosion though. I might check it again.

That smaller plug is a pretty-popular item for sale at electrical rebuilder parts houses.

Must be SOME reason......

Pop

i had the same thing over the winter...everything checked out like you, but my GPR was shorting inside the case. only reason i found it, i was messing around and after driving for a while the GPR terminal feeding the GPs was extremely hot..burnt my fingers pretty good. checked across the terminal and there was no resistance and i have continuity all the time(with key on anyway). try checking that...now i upgraded to a stancor...good luck

Well, didn't have a chance to touch my truck at all for the rest of the day. Tomorrow I should have time to take a look.

In the mean time, thanks for the input. Gives me some options to check.

It was the alternator. Swapped it out earlier today and no more battery light.

I checked all connections again, all the wiring, everything looked good. Never did hook up AE. I remembered that the alternator might have been under warranty, so I looked up my documentation and sure enough it was. Took it in, swapped it out, done.

I can vouch for this, I noticed my battery light flickered sporadicly and on exceleration and my volts were dropping. I hooked up my muiltimeter tester and wiggled the plug the amperage was eractic. Went down to the place where I had the Alt. rebuilt and bought a new plug, 4.50 out the door. And while talking to the owner walking out he said "Here, let me install that for you". Local rebuilders, Done by American's for Americans. ;)

99% of the time when that battery light flickers, it is the alternator. usually the regulator inside decides it wants to be temperamental. glad you got it fixed Curtis.

Overall, the most common failure with a 6G alternator is the field brushes reach end-of-life.

Since they are an almost integral part of the regulator, that is what gets replaced.

However, by the time the brushes have worn out, there are also deep grooves worn by them into the slip rings, so they need replacement, too.

Another thing that occasionally goes bad with 6G's is a diode will short. Less common is a diode going open.

Pop

I am having the same issue with the flickering light.
I have been told by many mechanics that have worked on Ford SD trucks, the pigtail that connects on top of alt(two wire plug) has a fault in design at plug and trips the light.
I am going to installa new plug/pigtail soon
Both batteries test good and so does alternator

Where does that one black plug that I replaced go to on top of the alt, meaning whats directly under there where that plugs into??? Mines still trippin the battery light on exceleration and for about 8 miles it trips on sporadicly with pedal action until it seems like it heats up temp wise and the batt light goes out and the volts return to normal.

It plugs directly into the regulator module.
https://www.ford-trucks.com/user_gal...id=243315&.jpg

Pop

I had the flickering light on rebuild alternator coming just 3 days after purchase. Mysteriously it would appear at high rpm and go off at lower rpm.
As Murphy law says the alternator passed bench test at NAPA with flying colors, so I was struggling with it for 3 months before it definitely gave up.
At final arrangements -turned out that NAPA sold non-NAPA alternator and buying it 150 miles from home I bought it from different NAPA chain than my local folks are and they could not honor the replacement warranty. Good thing I was going 150 miles away from home again and got the refund at NAPA story that belongs to the chain that sold me the rebuild alternator.