So the other day I was driving to work, and when I was getting off the freeway, the radio started fritzing out, getting all fuzzy, and dim. Well when I got off work, I went out and tried to start my truck, and the battery was dead. I had my buddy jump me, and it ran for about 20 seconds, then it just died. I jumped it again, and I noticed the battery light was on, then the gauges died, and so did the truck. The next day, I replaced the alternator, with a new one from Autozone that I had them test, and I replaced the 6 year old original battery, with a new Optima battery. The truck started right up, but the battery light remained on. I was able to drive home, about 15 miles on the freeway, at night with my lights on etc. without any problems, the voltage gauge stayed steady, slightly over halfway up, and never dipped or anything. I just cant figure out why the darn battery light will not go off. If anyone has an idea, it would sure help. Thanks!

 

There should be a very large capacity fuse in the charge line to the battery and another small 20 amp fuse to the alternator. Bet one or both are ka-put.

 

The battery light is on because the alternator is not outputing. The most likely candidate is a wiring issue:
A.check the regulator connector (3 pin) and 1 pin for corrosion
B. unplug the 3 pin regulator connector and check the following with key in the ignition in the run position with the engine off. check for battery voltage on the alternator b+ stud and the first and third pin of the regulator harness.
If no voltage, then check the harness for damage which may have blown the fuses.

 

Ok, So I have looked all in the engine bay for the mega-fuse, and I cannot find it anywhere, I looked in the pdb for the 20 amp fuse, and it appears good, but I can't find the other. Here is a couple pictures of both sides of the firewall. If someone could maybe point out someplace I am not looking. It is a 99' F250 Light Duty with the 5.4L engine.

 

On a 250 I don't know where it is located but you can follow the heavy lead from the alternator right to where it is. It may also be a fuse link in the line.

 

Its under the cover on the firewall right in front of your negative cable. Ford's are real bad for not charging over the slightest problem. Check your battery wires, connections to the starter and your wiring harness from your alternator. I've had to replace all of those along with the battery and alternator twice in the past 5 years.

 

Hope you figure it out, but while your at it you might want to clean that engine a little bit, looks a little dirty, and that could be messing up some wire connections.

 

Ok, So here is an update, My truck is still sitting in my driveway still trying to figure this thing out. Which really is a pain because I got caught in the rain a few times on my motorcycle. I cleaned out the engine compartment... Looks all nice now, I cleaned all of the connections. I still cannot seem to figure out where the mega fuse is located. In any case, I took out the new alternator and brought it to another auto zone, and had the guy test it, he said it was bad, and gave me a replacement that he tested good, I put that one in and....... no dice. Still with the charge light. Son of a.... So now I am wondering if anyone has a recomendation for a place in or around Mesa, AZ to bring it that deals with electrical pains.... thanks

 

Did you do what Mike said in (B.) ???
Also I do not think you have a Fuse, I think you have a 12 GA Gray Fuse Link J.
Only by doing what Mike said at the B+ stud will you know.

 

i had tha same problem and it was a fuse that was in a box located to the left of the battery...got it fixed yesterday

 

I bought a multimeter and went under the the hood tonight, I did as Mike said, and tested the voltage at the B+ stud tested just under 12 volts, Same thing for both of the pins in the regulator harness. I checked all of the fuses in the power distriubution box, and found one fuse a 25a that was blown, I replaced it, and the battery light is still on when I run the truck. So, at this point I went inside and had a beer and gave up for the night. If there are any other ideas on what it may be. It would be great.

 

C1 CHECK FOR OPEN A CIRCUIT

* Measure voltage at test point A on the voltage regulator.
* Is voltage at test point A equal to battery voltage?

Yes
GO to «C2».

No
CHECK fuse in Circuit 36 (Y/W) and REPLACE if required. If OK, SERVICE open in Circuit 36 (Y/W).

C2 CHECK FOR SHORTED I CIRCUIT

* Remove three-pin generator regulator connector.
* Turn ignition switch to RUN position.
* Is indicator lamp on?

Yes
SERVICE short to ground in Circuit 904 (LG/R).

No
GO to «C3».

C3 CHECK S CIRCUIT FUNCTION

* Install generator regulator connector.
* Remove one-pin S connector.
* Connect wiring harness S terminal, Circuit 4 (W/BK) to the positive (+) battery post using a jumper wire.
* Is indicator lamp on?

Yes
REMOVE jumper wire. GO to «C4».

No
REMOVE jumper wire. GO to «C5».

C4 CHECK FOR OPEN S CIRCUIT

* Remove three-pin generator regulator connector.
* Measure wiring resistance between the one-pin S connector and the S (center) pin of the generator regulator connector.
* Is resistance greater than 1 ohm?

Yes
SERVICE open or excess resistance in Circuit 4 (W/BK).

No
CHECK for loose or bent pin in voltage regulator or connector. If OK, REPLACE voltage regulator.

C5 CHECK STATOR OUTPUT VOLTAGE

* Start engine.
* Measure voltage at the S terminal on the back of the generator.

*l Is voltage at least 1/2 of battery voltage?

Yes
GO to «C6».

No
GO to «Pinpoint Test L» to FIND the cause of low generator output.

C6 CHECK GENERATOR OUTPUT VOLTAGE

* Measure voltage at the B+ terminal on the back of the generator with the engine running at 2000 rpm and all accessories turned OFF.
* Is voltage greater than 15.5 V?

Yes
GO to «Pinpoint Test B» to FIND the cause of high output voltage.

No
REPLACE voltage regulator.




I hope this helps

 

I have had various problems over the years with my truck not charging so I can give you some things to check. You have alreay replaced the alternator and battery so you have a good head start.

First thing you should check are your battery cables. The first time I had a problem with starting my positive cable had coroded and broken at the starter. Check it, clean and replace it if its bad.

Next check your alternator wiring harness, it could be bad as well.

I'm going to warn you, if you have to get either one it can only be gotten at Ford. The battery cables are well over $100. The wiring harness is around $60. The wiring harness comes with the mega fuse which attaches to the fire wall beside your negative battery cable.

One other thing you can check, its a long shot but check the tension on your belt. If its not tight enough it your battery light will come on as well. Good luck and let us know if you find anything.

 

OK, so here are the results of the checklist,

So What I am thinking is, I will take the alternator off, and bring it to another auto zone, and have it tested again, to rule out the regulator issue, if that tests good, I will probably try replacing the alternator harness. Unless you guys have any other Ideas what to check.. Thanks for all your help by the way.

 

Without going back thru all the replies, your drawing does not show the 20 amp small fuse but neither here nor there at this point.
The charge lite is put out when the alternator charge voltage comes up to a certain value.
This says either the alternator or the regulating unit is possibly at fault.
Start the truck and check if you see at least 15 volts at the battery by raising the idle by hand. This tells you if the alternator is outputting.
If it doesnot rise you have a fault with the charging unit.
Could be the harness or connectors, open fuse link.
Do the same test on the alternator side of the fuse link if there was no rise at the battery. This tells you the link is open if you see the voltage rise at that point.
Theres' not much else to have a problem with.