The past few weeks the dashboard warning light for my alternator/battery will occasionally light up while driving down the road. Whenever it does, my plug in voltage meter shows a healthy 14.x reading. It usually goes out after a few seconds, but will stay lit up for as much as thirty seconds.

So other than voltage being too high or too low, what else will cause the dash trouble light to illuminate?

Stewart

 

The Lamp is illuminated when a circuit from the Alternator to the Lamp "Opens". What I have found when this occurs )providing, like yours, the Alternator is outputting within Specifications) is the wire from the Alternator is chafed on the D/S Valve Cover and/or the Pins in the Fuse Block are corroded.


Hope this lends to a successful outcome.

 

Mine did that for about 6 weeks before the alternator quit. Did it both on my 6.0 and this 7.3

 

How long has the truck been running at this point? And what is the .xx value? Big difference in 0.1 and .099.

Most of the time that light means alternator. Either charging too high or too low. But if the batteries are in good shape, the voltage regulator should drop down below the 14.xx charging rate after a short period.

I'd check the specific gravity of each cell of both batteries (floating ball tester thingy) and put them on a trickle charge overnight to rule out the batteries.

 

when my 02 does that i have to push the 2 wire plug into the alternator. every now and then it loosens up enough to loose connection and turn the light on.

 

The ONLY thing that bulb connects to is the voltage regulator in the alternator. The ONLY thing that can cause the light to illuminate is a ground path through the wire. I'm not sure SMT_FORD knows the difference between a shorted and an open circuit but disconecting the wire anywhere (open) will not cause the light to illuminate. In Tom's case, I think he should read the next paragraph. Actually, in his case (02), the PCM controls the alternator excite wire instead of 12v through the bulb filament in key-on so there IS the possibility of a loose connection.

What you may want to do (because it's free) is disassemble the alternator and tighten the screws that attach the regulator to the case. They have a habit of loosening and then the regulator has no idea what the voltage output is (no reliable ground baseline) so it grounds the circuit for the bulb and your light comes on. Try to remember if it happens under a certain load or at a certain RPM. Certain engine harmonics can really aggravate the concern.

 

I changed out the plug at the alternator when mine did that and it resolved the issue. O'Reilly's was damn proud of that plug though, but it was made better than the OEM.

 

Can't tell from your post, but I'm guessing this is one the changes that occurred in the 02 and up models? The 01 and earlier are different?

I wonder how many "lifetime" alternators I've replaced due to a loose voltage regulator? And how many sets of batteries ended up being replaced shortly afterward as a result?

I've pulled them apart before to check the condition of the brushes, but never thought to check for loose screws on the voltage regulator.

I miss the days that was separate from the alternator and only cost $5 or so. (Seems like the alternator was only around $30 then, but combine the two in one case and it becomes a hundred dollar bill).

 

I remember reading that you should NEVER disconnect the alternator when the engine is running or the key is in the on position....

Maybe someone else can chime in why?

 

My 2000 7.3 did this last year and I could tap it with a wrench lightly and light would go out. Something was sticking in my opinion, installed new alternator and cured problem.
Check voltage when light is glowing and check it when light is off should see a difference.

 

correct. the battery is a load to the regulator. if it is disconnected, the regulator goes full power, and can put out extremely high voltage frying all your electronics.

 

Mine was the alternator itself.

 

Thanks! I didn't remember the details, just filed it in the gray room as "B.A.D"

 

The run-time when the light illuminates varies.

14.0 to 14.2 usually, when the light comes on. Sometimes it will drop to 13.8 volts.

The batteries are in excellent shape, in my opinion, based on how they responded during my CPS problem on the dunes.

They are yellow top Optima batteries.

Thanks Cody, I'll try this.

It will happen at all RPM's, whether driving down the freeway, stop-and-go city driving, or sitting at a stop light at idle.

Different input on the go-pedal (whether moving at speed or stopped) doesn't change anything.

I've been wanting to try and rebuild my own alternator anyway, so doing what Cody suggested will help me get off my tushie and get started.

Stewart

 

Piece of cake. Just make sure to find a toothpick for reassembly.