On occaison, my battery light will come on while driving. Volt meter shows good 14v or so. Had battery and alt tested and both passed. First time i noticed it, it would go off once i got above half throttle and then kinda flash a little bit and then just come back on strong as i started to coast. Down shifted to 4th gear and revved the engine more and never came on. Went back to 5th and same thing. Was only on for 10 miles or so and gone for the rest of the day. And it wasnt like a "normal" flash with set time on and off. More like it just wasnt sure there was a problem and would come on for varying lengths of time before finally deciding to come on.

Next time i seen it, tried the same thing and didnt matter what i did, just stayed on for a while with the occaisonal "flash" and then off again never to come back on. Since then sometimes revving will make it go away and others just on no matter what.

Everytime runnin down the freeway but i dont recall it ever coming on at night with lights on. Just daytime hours headlights off.

No additional electrical addons to the truck other than a set of foglights that are tied in so they only work with high beams on. When the light does come on, there is nothing weird happening to the truck's performance or loss/gain of volts on the meter or anything like that. Just the light come on and go away eventually. The last time it did it, I pushed in the clutch so the engine went back to idle speed and light stayed on so i pulled over and was going to use the handheld voltmeter I had brought but by the time i got stopped the light was off. Is the in-dash volt meter accurate and reliable enough to assume if its showing 14v thats what i have? Any thoughts?

 

Oh and I havent really paid too much attention into time frame but from a few of the trips i remember it happened roughly 45 minutes into the nearly hour trip. Would assume if it was dead battery, should've occured at start of trip and then went away as alt charged it back up. Havent gotten around to putting a trickle charger on the truck just to see if that solves the problem but the guy did say battery was good. The purchase stickers on the battery werent notched so im not sure of its age and doubt its the original battery from 2000.

 

I had the same thing happened on my V10 Excursion. I swapped out the alternator and that fixed it.

I did the same thing you did. Try to check the voltage while running and it was ok. When the light came on, I tried pulling over to measure it, but the then the light would go off and showed normal. Really frustrating.

Make sure you clean the battery terminals good, too. After changing the alternator, get your battery charged up.

 

That light is triggered by the regulator - if the regulator THINKS there is something wrong, it'll light that light.

It could be a bad diode inside the alternator that's causing AC to pass through to the regulator and it's getting confused.

Either way, unless there is something wrong with external wiring (unlikely in your case) another alternator will most likely cure it.

 

Perfect. Another repair on a truck I just bought. Why cant everything go wrong on the test drive not a month later lol. Well anyways thanks for the input. I was thinking I would end up replacing the alternator. May get lucky and find out the current one is the Autozone brand with the lifetime warranty and I wont have to spend any money this time .

 

I think the Autozone warranty only applies to the original owner...not when the vehicle is sold to someone else. You can check, but I believe that is the case.

 

So I guess I never posted a reply from the original issue last May. I pulled off the battery wires, cleaned them all up and fiddled with all the electrical wires I could find under the hood ensuring they were all all snug and not loose losing connection. Not sure which thing was the problem but the light never came back on ... till last week.

Light came back on when I was headed home from camping and I planned to do all the above mentioned items again assuming that it was the same issue again but after unloading the quads and all the camping gear I was ready to just relax and then forgot about it. Truck sat two days and next time I drove it was to head out of town for work. Noticed the light was on, still assuming it was the original issue, just ignored it thinking I would fiddle with it when I got a chance since I was already late leaving town. Made it 40 miles into the 160 mile drive and the truck instantly lost all power. The more gas I gave it, the more it bogged down and the slower it went. For some reason, I flipped off my high beams to low beams and the truck roared off again like nothing was wrong (cruise was still on). Shocked, I flipped the high beams on and again the truck lost all power. I was about 5 miles from the next town so I just continued on with the low beams. By the time, I made it to town I could only drive with the park lights on. I shut the truck off in the gas station parking lot and tried to start it right back up but didnt have enough juice to crank the motor. I hooked up my jump box to the battery and the truck started right up. With the truck running at an idle hooked up to the jumpbox, I had 11.1 volts. I turned on the high beams and it fell to 9.9 volts but stayed running. I shut the truck off and called AAA to tow the truck home and the wife to come get me and take me to work. About a half hour later, I decided to turn the truck around assuming the tow truck driver would want to load it facing forwards. I hooked the jump box back to the battery and used that for battery power to turn the truck around (battery light still on with the engine running). Shortly after I shut the truck off, the wife arrived and said "so it wont even start?" like she was gonna try and diagnose the problem. I replied with a "nope" and since I was sitting in the driver's seat already I turned the key to show her and of course, the truck started and the battery light was off. It was a weak start from the dead battery but still started on it's own. Seeing the in-dash pos volt meter up in the normal spot and the battery light off, I checked the battery and was over 12 volts. Hoping the alternator would work the rest of the way, I continued the drive to work. The truck drove the rest of the way without issue and when I arrived the battery was showing 14.2 volts at idle.

Next day I started the truck and the battery light was back on so I went to NAPA to have them test the alternator. All they had was some little handheld device which the lady input the battery info into it and connected the wires to the battery with the engine off and it said was the battery was bad. I asked her if they could check the alternator because I was pretty sure that was the problem and she said she could check the charging system to see if there is a problem but couldnt test the alternator itself or even tell what the problem was. It would just identify if there was a problem or not. She hooked the device back up and this time it said the battery was good. I started the truck and her handheld said the charging system was good although she was only showing 12.3 volts at idle. I mentioned 12.3 seemed kinda low if the charging system was working properly and she said something to the effect that it's a 12 volt system so I just said okay and left it at that.

I've driven the truck on short trips around town here 2 more times this weekend. Battery light is on but no issues starting or driving, at least not yet.

So my question is battery or alternator? Or something else? Can the battery go so bad to cause my problems and then suddenly fix itself and accept a charge from the alternator and charge up fully then go back to being bad again but not so bad that I can still start it? Or is it more likely the alternator is crashing and I just got lucky that it worked again and got me to work without being towed home.

If it is the alternator, is there any reason not to get the 130 amp instead of the 90 amp?

 

12.3 volts on a unhooked battery is only 60-70% charged. 12.6V is fully charged. The NAPA lady doesnt know much. With the truck idling it should be reading upwards of 14v, especially if it is charging a weak battery. Sounds like the alternator is bad, which would lead to the battery wearing out also.

The fact that your truck wouldnt run with the high beams on and then only the parking lights makes sense. Once the alternator goes and the truck is running on the battery only. In a properly running setup, the battery is only used as a starting battery, then the alternator tops it off and continues to run the cars electronics.

Could be the internal regulator being bad, or the alternator itself, but If possible I fould find a store that could actually test the alternator, or just replace it.

And unless you have a lot of high current aftermarket stuff, i.e. lights, stereo etc, the 90 amp should be fine.

 

So I dont know if this is related but my fuel gauge is no longer working. Before i left town the other night when my alt/battery issues occurred, i filled up with gas and the truck took about ten more gallons than I expected based on the gauge's position but I didnt think much of it. The gauge did go back up with the fill up. Now I have about 170 miles on the tank and the gauge is still above the full mark. I would guess the gauge stopped working about the same time the battery light came on or maybe a little before. Probably a coincidence but not sure. Is there a fuse that runs just the fuel gauge and sending unit? All the other gauges are working like normal. Is the sender unit hard to pull to test/replace? Any thing else I should check?

 

Oh and that night in the gas station parking lot, i did replace the #3 fuse under the dash for the cigarette lighter and OBD II. Noticed that because I tried check

 

Oh and that night in the gas station parking lot, i did replace the #3 fuse under the dash for the cigarette lighter and OBD II. Noticed that because I tried check for error codes