Craig58
Registered User
Have been having an issue with the battery light flickering and not sure what to fix...had alternator and battery checked, both tested good. Any ideas of where to go next? Thanks
Flickering battery light
- Thread starter Craig58
- Start date
TNBrett
Full Access Member
Check connections at the alternator, voltage regulator, and the 4 pin connector near the regulator. Also verify a good ground to the case of the alternator and the regulator. I had similar issues with mine at one time, and had to do some repairs to a couple of wires at the 4 pin connector.
Big Bart
Tow&Slow
It is very common for the brushes to cause flicker on these trucks. The brushes can get stuck/not drop or to just wear wear out over time. Either will cause the light to flicker when it makes partial contact. (Sometimes at idle but not at higher rpms.) I have not heard of a bad regulator causing a flicker but others can weigh in.
So start as mentioned above. If your wiring all checks out and the flickering continues it is likely the alternator. If you replace it replace the regulator too. (Always replace as a set.) I had a hard time finding the correct alternator and ended up at Napa who got one overnighted in.
Also check the ground from the regulator. It has one or two slide connectors in the middle that can become corroded as I recall.
Many alt testers just test the amps and voltage at full field and at high rpm off the alt. So at +13.5v and say 50 amps it says pass. But not all have a alt light or other way to test for that flicker at slow rpms. (Or the tester does not hook it up.). So flicker or not it may be able to produce power, but its on the way out.
So start as mentioned above. If your wiring all checks out and the flickering continues it is likely the alternator. If you replace it replace the regulator too. (Always replace as a set.) I had a hard time finding the correct alternator and ended up at Napa who got one overnighted in.
Also check the ground from the regulator. It has one or two slide connectors in the middle that can become corroded as I recall.
Many alt testers just test the amps and voltage at full field and at high rpm off the alt. So at +13.5v and say 50 amps it says pass. But not all have a alt light or other way to test for that flicker at slow rpms. (Or the tester does not hook it up.). So flicker or not it may be able to produce power, but its on the way out.
There's a grey plastic plug (if I remember) on the top / back of the alternator. The wires become loose inside the plug. If the bat light is on while idling, have someone watch the dash while you wiggle that grey plug. If the light goes out you found the problem. Also consider doing the 3g swap and headlight wiring harness upgrade if you're planning to keep the truck. Both upgrades are great for simplifying the charging system and protecting your existing electrical system from damage.
^^^^^^^^^^^^^^^^^^This absolutely. I made all new cables for the 3g swap so it was a hair more complicated than JY swapping but still quite easy.
Big Bart
Tow&Slow
Did you figure it out?
Craig58
Registered User
Big Bart
I have just now got back to it and no, I haven't figured it out yet. Still have the battery light on but have one more thing I noticed. At speeds above 60 mph it goes off? As soon as I let off the throttle it comes back on....I checked the plug on the top back of the alternator already, it was a trouble spot in the past. But it checked ok visually, unplugged it and reseated it checking the wire connections. Truck cranks up very quickly so I know it's being charged when it's running. The volt meter is only reading 12 volts though... I'm out of ideas and don't want to replace parts unless I can prove they're bad. Any more help would be much appreciated...
I have just now got back to it and no, I haven't figured it out yet. Still have the battery light on but have one more thing I noticed. At speeds above 60 mph it goes off? As soon as I let off the throttle it comes back on....I checked the plug on the top back of the alternator already, it was a trouble spot in the past. But it checked ok visually, unplugged it and reseated it checking the wire connections. Truck cranks up very quickly so I know it's being charged when it's running. The volt meter is only reading 12 volts though... I'm out of ideas and don't want to replace parts unless I can prove they're bad. Any more help would be much appreciated...
Big Bart
Tow&Slow
Here are some options that may resolve your issue and some testing to confirm.
Likely at high rpm the alt is putting out over 13v and the light goes out, then you drop rpm, voltage drops and light is back on. The truck should show a minimum of +13v once off idle. More like 14v at say 2,000 rpm.
1) Pull and clean all the connections on the alternator and the regulator. Check the ground wire from the regulator, it has one or two slide connectors in the wire before it grounds with a screw. If that ground is weak or not working it will set off the alt light. Pull the slide connectors and clean and reinstall.
2) Remove and clean all the connections on the starter solenoid on the fender well, the side with +4 wires going to it. Unplug both positive terminals on the battery first. Check the wire from the positive side of the battery to the solenoid is in tip top shape and the fusible link from the solenoid to the alt is in top top shape. Ohm test them to see if they are compromised internally.(Low resistance.) Plug the batteries back in and see if the post with the wires on the starter solenoid is close to battery voltage. Test the bat terminal on the alternator to check the same. You are insuring those wires are making a connection to the battery.
3) You can take your regulator and alternator to a parts store for testing. If they have a modern day computer style tester they can test both. If they have the old school manual style they only can test the alternator. Ask them if the alt or reg tests bad if you can buy both return the new/rebuilt ones if they do not solve your issue. Keep your old ones and bring it back later for the core charge if the light goes off. You always want to buy a new regulator with a néw alternator.
When the brushes start to go bad the light goes on and off as you suggest. It also still charges the batteries. (Just not as well.) But for how long know one knows. So if your wiring is now all inspected and clean likely you do have a alt or reg issue.
Now many members on this site have now suggested a 3g upgrade is a better way to go. It has a built in regulator in the alternator and has more output. It fits without having to do any changes. It requires a little wiring kit to install. Something to research and think about.
Likely at high rpm the alt is putting out over 13v and the light goes out, then you drop rpm, voltage drops and light is back on. The truck should show a minimum of +13v once off idle. More like 14v at say 2,000 rpm.
1) Pull and clean all the connections on the alternator and the regulator. Check the ground wire from the regulator, it has one or two slide connectors in the wire before it grounds with a screw. If that ground is weak or not working it will set off the alt light. Pull the slide connectors and clean and reinstall.
2) Remove and clean all the connections on the starter solenoid on the fender well, the side with +4 wires going to it. Unplug both positive terminals on the battery first. Check the wire from the positive side of the battery to the solenoid is in tip top shape and the fusible link from the solenoid to the alt is in top top shape. Ohm test them to see if they are compromised internally.(Low resistance.) Plug the batteries back in and see if the post with the wires on the starter solenoid is close to battery voltage. Test the bat terminal on the alternator to check the same. You are insuring those wires are making a connection to the battery.
3) You can take your regulator and alternator to a parts store for testing. If they have a modern day computer style tester they can test both. If they have the old school manual style they only can test the alternator. Ask them if the alt or reg tests bad if you can buy both return the new/rebuilt ones if they do not solve your issue. Keep your old ones and bring it back later for the core charge if the light goes off. You always want to buy a new regulator with a néw alternator.
When the brushes start to go bad the light goes on and off as you suggest. It also still charges the batteries. (Just not as well.) But for how long know one knows. So if your wiring is now all inspected and clean likely you do have a alt or reg issue.
Now many members on this site have now suggested a 3g upgrade is a better way to go. It has a built in regulator in the alternator and has more output. It fits without having to do any changes. It requires a little wiring kit to install. Something to research and think about.
Last edited:
Craig58
Registered User
Thank you for the information Big Bart! Will start at the top and work down your list. The man that used to rebuild all my alternators has long been passed on. He was a true blessing while here on this earth. But finding this site with so many willing to share their knowledge is also a god send. Appreciate your time and patience...
Big Bart
Tow&Slow
We had a great rebuilder here in town, they did great work, owner retired and his kids who worked for him passed on taking over the business.
So back to craappyyy auto parts store rebuilds. Took 3 try’s to get one that worked on my sons Galaxie. I try to order Motorcraft and AC Delco rebuilds when I can, but usually only available for newer cars.
Old Goat
Full Access Member
Same here, had a large rebuild shop in San Jose, Ca. back in the 80`s, did great work. Guy retired was sold to another guy. That lasted a few years, next time I went there, it was gone.
Now its the krappy auto part store rebuilds.
needed one for the 86 f250 5.5 years back. Went through 3 out of the box, and all had dry bearings when spinning the pulley. 4th one was a winner and has 86K miles on it so far. And this is the G1 Alt.
There are 3 part #s for the 86, difference is how it is clocked, IE where the electric plug lines up. 9, 12 or 3 O`clock. R111605A.
When this one gets tired, It`s getting the G3..
Goat
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