A problem I had last year on my 2000 F350 7.3L PS that took a couple of months to find was my batteries going down while parked, alternator not charging, battery light flickering on and off while engine was running.

Remove the breather box and breather hose going to the turbocharger. Look down at the left valve cover. The alternator wire is in the large wiring harness going from the top of the engine that loops down and come back up to the power fuse box mounted on the driver's side inner fender. There is a large 24 pin connection (plug/receptacle) held together with a bolt right at the middle of the valve cover. Unscrew that bolt to disconnect the plug and turn each end over so that you can see the bottom of the wires. Examine each wire closely to see if any insulation has been rubbed. You may not see any exposed copper wire but fire could be jumping if it is cracked or thin causing it to short out intermittently on the valve cover while the engine is running. This will cause your battery light to flicker and cause your alternator not to charge properly. When the engine is not running, the short will be a steady draw from your batteries pulling them down. Your alternator wire is on the bottom row of pins and has either green or orange insulation, I can't remember which, both colors on mine were compromised. If the insulation has been compromised, an inch of electrical tape will do the repair on each wire and your alternator will work correctly then. Make certain to wrap each wire separately that has any sign of rubbing before you reconnect the plug. Reconnect the plug and start your engine. Let the engine idle for 2 to 3 minutes before you check your alternator output. If that solved your problem, kill the engine, disconnect the plug again and wrap with electrical tape from the plug back to the outer protective cover of the wiring harness so there won't be any exposed wires that could be compromised in the future. Reconnect, crank the engine and test the alternator output again.

Sorry for the long post. Hope someone finds this helpful if it is not your problem.

 

any updates

 

none yet, still experiencing the same issues. Finally got one project out of the shop on Sunday so I hope to get my truck in this week, going to go over wiring again, replace the 2-wire connector to the alternator, and take a look at the brushes as was suggested.

 

I repaired a late 99 last week for a flicker battery light and the owner stated he had replaced the alternator twice in six months and replaced the batteries. When the truck arrived I verified the flickering battery light. I then load tested the batteries to be sure they were good. I then moved to the alternator, removed it and took to the local parts store for a bench test which revealed the alternator was good and passed. I then reinstalled the alternator and went to look at the wiring. Were the alternator wiring plugs into the alternator there are two wire that both showed chaffing and the wires were exposed I repair the wires and tied them back against the alternator cable to keep from moving. I then decided to replace the belt tensioner and idler pulley. Once removed both were original Ford parts with 158,000 miles on them. I assumed that the spring in the tensioner would no longer hold the correct tension and was causing the belt to slip which inturn caused the battery light to flicker.
The system is now charging at 14.3 volts and the battery light is out. It's been a week now and the trucks running fine. You may want to start with replacing the tensioner, pulley and belt if you haven't yet. Check the wiring too.

Jeff

 

Got the truck in the shop yesterday....Replace the 2-wire plug and ended up putting in a New alternator from Advanced Auto (Tough1 - made in China, not thrilled but needed some results). Drove around today for a few hours and the voltage never dropped below 14, I'll keep an eye on it this week and report back.

 

So you did two things to it to fix the problem.

Which one was it that did the trick?

Pop

 

Yeah, I hate messing with two variables at once.
The plug and wiring seemed to be in good condition (no corrosion or loose pins), I replaced it more for peace of mind as last time I took it off I broke the plastic clip that holds it into the alternator socket. So I'm going with the new alternator being the fix (but I'll really never know unless I throw the old one back on)

 

UPDATE: truck had been running and charging fine (consistent 14.1 or so) for the last few weeks, last night after a 20 minute drive I smelled something hot, like burning electrical - popped the hood and could see the glow coming from the back of the alternator - the stud was cherry red, charge wire insulation was melting/smoking and the alternator case itself was very hot. What does this mean? Bad alternator or bad charging wire?

Glowing stud with reflection off the IC pipe

Due to numerous bad reviews of the Tough1 Alternator, I had already ordered a 185 Amp OEM HO Alternator from DC Power last week , tracking says it will be here Monday but I dont want to install it if I have something else to fix first.

 

Looks like you had a campfire in the kindling stage.

A typical failure mode to see this would most likely be one or more shorted diodes.

That would take the batteries straight to ground. It's one of the reasons we have those fusible links in the wiring harness.

It's also the reason why those of us that have added the heavy-gauge wire from the alternator output post straight to the batteries should seriously consider adding a very-heavy in-line fuse to it.

Pop

 

forgot to mention that when this happened the output was showing <14 around 13.7 or so....

So replacing the alternator should remedy this?
Could I have something else going on that is causing the alternators to go?
Sounds like it may be prudent to upgrade the charge cable....what gauge and what size fuse should I use with the new 185 amp alternator?

 

Wait! The alternator is the only thing than can produce a voltage above that of a fully-charged battery (about 12.6 volts), so the alternator must be outputting.

The red-hot connection is from too much current passing through the connection, but now we can be reasonably sure it isn't going from the battery to ground through a faulty alternator. The reason for too much current draw must be elsewhere.

I have to assume that all the connections were tight at the time (though charred now), but if that connection was loose (even a loose crimp between the eyelet and its wire), it could cause that display.

Looseness causes arcing, which causes heating, which (in your case) causes "light"!

Pop

 

Also check this thingy-me-bob. It was the cause of my alternator failure.
At first glance all looked good. But when the electrician took the terminals off you could see the dis colorization from the arcing. Not saying thats ya problem but something to check.

 

Brian,

That's a fender-well mounted "solenoid" that takes the key's "start" current and multiplies it to drive the solenoid in the starter motor, which uses considerably more current than the key alone can handle.

HOW-SOME-EVER, I believe they discontinued the use of it at the same time they discontinued the use of the Mitsubishi PLGR (planetary-gear-reduction) starters. Ryan's 2002 may have the Nippondenso OSGR (off-set gear reduction) starter.

Just a thought.....

Pop

 

Well done Pop. Ryan , thats all I got so best of luck bruva

 

Ok, just to be sure, I went and looked up the wiring diagram for a 2002. It has a "Starter Relay" that does the same thing as the fender-well mounted solenoid, but it's shown as being in the Central Junction Box.

It's probably one of the typical Bosch-type relays if it's in there, so apparently the Nippondenso starter solenoid still draws a lot of current, just not-as-much as the Mitsubishi.

So, Brian, why does your Brazilian-made 2003 truck still have one? It's called the "Starter Motor Relay" on my 2000's diagram.

Little mysteries of the universe.......

... or maybe they were still using the Mitsu's in Brazil.

Pop