I've been lurking on the site without registering for quite some time. After using the suggestions already posted, I've tried to fix the problem in my charging system. I have a 2000 Lariat with the 5.4 and 140000 miles. My alternator went in May. Replaced it with a reman, and it worked for a month. I got a new reman under warrenty, that they bench tested good before I left the shop. It was not working in the truck. I then changed the grounds from the battery to the block to the frame. I changed the harness that goes into the back of the alternator with new connectors. I spliced the other end together, and took the connector out of the loop. I changed the mini fuse in the fuse block. For awhile it seemed that it was okay. Then sometimes the light would be on then others it wouldn't. Finally it came on and stayed on. I just got another reman under warrenty and the light didn't go off. I looked for the mega fuses mentioned in other posts, but the wire from the alternator goes straight through with no fuses. The fusible links are okay. For some reason the alternator doesn't seem to be turning on. Sorry for the long post, but I am baffled, and couldn't find the answer anywhere on the forums. Thanks in advance.

Don

 

Unless you have some different wireing option, there are no fuse links.
Starting from the battery a lead goes to the starter motor relay, from there through a Mega fuse to the Alternator.
The Mega fuse in on the firewall near the battery.
There is a mini 20 amp fuse to the alternator winding.
A lead from the Alternator goes to the insturment panel charge indicator then to 10 amp fuse then to the ignition switch which powers the Alternator winding at start up and run.
When the Alternator output rises to a certain point, the charge lamp loses it's ground from the Alternator and goes out indicating the Alternator is working.
Seems you have an intermitant issue that is not the Alternator.
Do not bypass any fuses.
A lead loose, a fuse with high resistance, ignition switch etc are suspect.
Look at a Haynes book #36059, page 12-17 for the overall wireing lay out.
Not that there could not be difference but this is the general layout.
Good luck.

 

On the wire from the battery to the firewall there is a fusible link. Then all the posts say there is a mega fuse, but there isn't one located where it shows in the book/posts. Where the wire with the fusible links connects to the solenoid, the line from the alternator comes in. I didn't/wouldn't bypass a fuse. I cut a wire connector and wired them together just in case the connector was bad. Where is the 10 amp fuse located/labeled? I couldn't find any other alternator fuses in the manual. I replaced the one in the engine compartment which was a 20 amp. Thanks again

Don

 

Your discribing wireing that is quite different than the norm so we are not going to dissagree with you.
I have a 2002 with normal known wireing.
The Haynes book shows the wireing as it is. Sometimes I see errors but not the this extent.
If it comes and goes, it must be correct but a connect problem at some point.
Good luck.

 

The only thing that I know is different is the lack of mega fuses between the alt and solenoid. I have seen some people talking about the fusible links on the battery cable. I wouldn't mind eliminating the other issue you talked about earlier. Where is the 10 amp fuse that was mentioned in the first post, my manual doesn't list anything other than the 20 in the main box under the hood. Thanks again

Don

 

How's the battery? Newish, original? There is that or the alt field fuse underhood, which if it was gone probably wouldn't of been a here and there issue. Any corrosion on the battery posts? Just some more ideas, hope it helps.

 

Make a test to see what you have when the charge light is on.
Measure the voltage at the battery terminal with the motor running.
If 14.5 volts +/- or above and the light is on, that indicates only, that the lamp lead is getting a ground from some place other than the alternator regulator or a circuit in the regulator is faulty. This would narrow down the issue to only the lamp lead circuit.
If you see about 12 volts +/- with no sign of change as the motor runs, the alternator is not outputting under it's regulator control and grounding the lamp lead as it normally would.
Notes; once the alternator begins to charge, the charge circut lamp is no longer needed so the regulator circuit opens the ground to the lamp and it goes off until either something happens with the charge circuit that grounds the lamp circuit again or the ignition switch is switched off, alternator speed falls below a certain speed before the ignition switch is turned back on or a re-start occurrs. This action is your indication of a charge issue even if the output may be low or some other issue is present.
Try to look at this from these stand points and ID what might be going on.
Reguardless of what physical wireing you have, the systems all work the same way.
Another hint to a charge problem is slower cranking, headlights dim or changing brightness etc.
There are such things as one wire alternators but they still work the same in a different configuration.
Good luck.