This weekend, my battery light decided to flicker on and off while running. At first, it would go out under load, but come back on while at idle. Today, the light simply stayed on for the entire 65 mile drive. The batter gauge appeared to stay steady at around the 14 volt mark.
I have checked the connections at the batteries, and both sets are tight and do not wiggle. The truck starts up just fine.
What should I check next? Have the batteries tested? Have the alternator tested? What else could be causing this issue?
I do not know how old the batteries are, as I purchased the truck in October of last year.
Your help with this is much appreciated.

 

your alternator is toast.

 

Spokane, my old stomping ground. Like the weather over there - I hear you can see the sun.

Yes, looks like the alternator is on it's way out. If it's stock, might be good to have it rebuilt locally, as the quality of the aftermarket units can be hit or miss. Good to have the batteries checked, and if over 4 or 5 years old, you might consider replacing. Those cold Spokane winters will challenge the batts.

You could start with pulling the cables even though they are tight, and running a post cleaner brush on everything. They can get oxidized and not conduct as well.

There's some good recent threads on this site on folks that have upgraded to 140A and 200A alternators if you need more power, but there are some mods needed to do that safely. The stock 105-110A is plenty for most.

At that mileage, check the belt and tensioners...

 

When I had those symptoms, it was the alternator.

 

To be more specific, your voltage regulator is putting out a signal to the system that something is amiss. Even if you're charging up normally, there's still something going on within the regulator (internal on alternator)... and time doesn't have your back on this one.

There is one slim chance that you vave a wire shorted to ground (light green with a red trace)... but I'd file that in the "I Don't Think So" folder.

I had to change my alternator out this winter at 270K miles. Sorry for the bad news.

 

Thanks everyone for all the input. It appears as if the consensus here is the alternator went TU. Aside from having it rebuilt. What brand should I stick with? That might be a question like what oil is best, but thought I would ask anyway.
I will also check the drivebelt and see if that needs replacing while I'm at it. And oh ya, have the batteries checked.
Any other suggestions are still welcome.

 

when the one in old green went, it was replaced with one from oh-rye-lees.....

and gets changed out every 2 years now, almost like clockwork. good thing it's free replacement.

 

It's most likely your alt, but like Rich (tugly) said there's a slim chance it could be the green wire/red tracer. It's easy enough to check, esp. since you have to disconnect it to remove the alt. Just take your voltmeter, hook the neg lead to the neg. batt. terminal, stick the positive inside that 2 wire connected on the green wire side and see if you have a voltage reading. If you do, you know it's your alt. if you don't, it's a short/blown fuse and your alt. may be fine. I bought 3 alternators in the middle of the last snowstorm thinking I was getting rejects right out of the box. Once I finally checked that and figured out I had a short, I felt like an idiot.(Now I'm broadcasting it to the world). Took about 10 seconds to check, and can be done with the truck not running.

 

Jeb,
What kind of reading should I be seeing? I've got my voltmeter set to Vdc, and am getting of reading of 0.002 or less. Does that seem correct? Or am I screwed up on my setting?
If my setting and readings are correct, what is my next step to correct the short? Truck won't start today, so I'm stuck in the driveway until I get it fixed!
Please help!

 

Unplug the alternator and with your meter set to volts DC, connect your red probe on the wire that is light green with a red trace, and the black probe on a good ground. Make certain you have good electrical connection to both. Turn your ignition key to run, but do not start the truck. If you have 12 volts on the meter, your alternator is triggering the light. If you do not have 12 volts, it's party (and troubleshooting) time.

 

Thanks for the reply. Turning the key on is a great idea . Thanks. Never crossed my mind. I am getting 12V to the orange wire without the truck running. I'll give it a shot. Have the alternator ready to go.

 

Turn truck on (but not started) and got a 10.15 reading off the battery, and 9.95 reading on the green/red wire. Does that sound about right?
Assuming so, I'm moving on the alternator.

 

It appears to have worked!
I replaced the alternator, and she fired right up...well about as well as on weak batteries. Drove her for about 20 minutes. All seems to be working properly. No more light.
Thanks to everyone on here for the help. This site is awesome. The people are the best. I could not have done this without your help and insight.
Thank you all.

 

Woohoo! Looking at those voltages, you were driving on battery reserve and you were close to being shut down. Great job!

 

The truck didn't want to start this morning, when I wanted to pull her to the back to work on her. Probably killed her trying to start. Glad I made her home yesterday after getting fuel. Would have hated for her to die at the station...in the middle of nowhere.
Thanks again for all your help.