First of all thanks in advance for any help, here's the story. A few days ago my battery light came on and went off randomly. Still started and ran fine however last night when returning home I noticed the battery level dropping until the radio and lights started to flicker. When I hit the gas the gauge shot up to normal, got home and shut it off. Started it again immediately and it barely started. Tried again this morning and of course no go. I figured it was the battery or the Alternator so I removed both. I got the alternator tested and was told it was good to go. The battery was reading 11.5 volts but slowly trickled down when reading the Ohm meter. I bought a new battery and installed the old alternator. Truck started but battery light is still on. Gauge reads normal. So what to check next? Lastly, I am no mechanic by any any means but handy with tools and can follow directions, somewhat. So any advice I get will in turn cause me to look through my Haynes manual to find the parts, lol. The truck is old enough that it pains me to throw allot of money into for expensive labor and parts. I am willing to tinker with and hopefully someone here is willing to guide me in the right direction. Thanks.

Edit, I did read the guide where it says, "Tell us about your truck" but forgot. It is a 2000 F-150, 4x2 V-6 with approx. 133K

 

On the firewall right next to the battery is a cover for the battery and alternator connections, On my truck(97 F-150 V6) there are a type of fuse(2) at these locations, I would check the one that the alternator is connected to, Do a resistance test or check the voltage at this location with engine off and then engine running to make sure that the output from the alternator is getting back to the battery.

I would also recheck the alternator with a voltmeter(with engine running) to make sure that it is putting out around 13 volts or a little more.

These are simple things that can be checked fairly easilly.

Val

 

that new battery could have a bad cell... or you could have bad diodes in your alternator... or...check every last connection in the battery/ charging system and i bet you will find your problem..

 

be certain the belt is not slipping

 

The truck started fine this morning and Battery light went out for about 10 km then came back on, Voltage held steady. I will check all the connections but,
1. How do I test the Alternator Voltage, just meter the battary when running? Should be around 14v, right? Does it need to be high idle and will it fluctuate?

2. The belt is showing signs of wear but I don't think it's slipping, is thier any way to check? Tension seems good.

 

Use a voltmeter on the battery, Check first with engine/switch off and then with engine running, Should be a 1-3 volt increase with engine running

There are indicators on your belt tensioner that indicate if the belt has stretched beyond its useful length.

Val

 

Tested with truck off and got 12.30 truck running and got 12.07, not good I am guessing. Now what? Is this confirmation that the alternator is shot? I tested from the back of the alternator to the positive and had continuity. Help, is thier anything else to check rather than replace the alternator?

 

I suggest taking the alternator off and taking it somewhere else to have it tested but if you are getting a lower voltage with the truck running than with off then it suggests that the alternator is not producing any output as you are actually droping voltage while it is running.

If it were a pre computerized vehicle you could start the truck and then disconnect the battery and if continued to run then the alt was working but with a computer I believe you would/could cause damage to the system.

Def sounds like an alt problem though.

Val

 

Check your grounds... If 1 is broke, or corroded, it will caus electrical; issues randomly or consistently.

Also I might add... your symptoms, are symptomatic with an irregular diode pattern, also. But when checking an alternator... The Diode will not always rear its ugly head. To be sure, I have had to stand there at the test machine, and have the test done 3 to 4 consecutive test before the failure occurs. The guy may be wanting to not do it, but I ask him to humor me, and then he will. Then when it fails, he will shrug it off, and say he never saw that before. It is very common though.

In short, a cool diode will operate, but once heated up, will faulter.

Grounds, diode, corroded wire/connection. Thats where I would start. Put a volt meter on the battery, and with the engine running wiggle wires around the alternator to see if voltage changes.

I have also heard of a corroded wire on the starter causing this to. ( the gear reduction type with the selenoid mounted to it)

 

Haynes Manual refers to checking a Alternator Feild Fuse? Where the heck do I find it?

I am a little rusty with inserting pics, but I will try and put one up later.

 

I have checked everything that has been suggested and everything seems good to go. I am off to get a new alternator tomorrow All the fuses seem good, connections tight, etc, and I am still losing voltage with the truck running. New Alternator and new belt going on tomorrow. Thanks and will let you know the results. Speaking of which, can I just wiggle the old belt off or the fan? Or do I need to remove something? Stupid question but I gotta ask.

 

You need to use a breaker bar to release tension on the belt from the belt tensioner then you can slip the belt off.

But if you already have had the alternator off then you already know that

Val

 

I have had the belt off the alternator before of course however I have not taken it off completly. Looks like I can work it off around the fan, hopefully as I would rather not take the fan off. That's a rather tight space to be working at.

 

Damn it all to hell!!! Took it all apart, alternator off, belt off and I don't have a 15/16th socket or box end wrench to get the pulley nut off!!!

 

So...........................I hitched a ride to work with a buddy and took the old alternator to work and took off the nut with an impact wrench. We picked up a couple cases of beer on the way home and tackled the job. The new alternator and belt were on within 2 beer!!!! Started the truck and still have a battery light!!!! Tested the battery, 12.2V turned on the truck, 11.5V!!!!!!! Cursed and stomped for a bit and realized that we forgot to hook any wires into the Alternator!!! Plugged her in and all was good, finished the beer and felt proud!!! Thanks for all the help!!!