I have had a very weird charging problem I cannot figure out.
Every once in awhile my truck would hard start or no start. Dead batteries. Jump start and truck would be fine for days, even weeks.
Then same thing again.
Never saw the charging light on the dash at all.
Jump started it once and threw a meter on it. 13.6+/- volts. I figured, alternator is ok.
Happened several more times. I changed alternator. Truck was fine for a few weeks.
NOW, I am beginning to see charging light on dash every once in awhile. Stays on for a few seconds at a time. Weird.
Load tested both batteries(Optima red tops bought new in 2009) Load test fine. Hmmmm. Ran temporary wire from alternator to battery to see if I had bad charging wire.
This morning, got in truck to move a trailer around. Charging light was on the whole time(10-15 minutes or so).
Shut truck off. No start. Batteries dead.
Jump started. Light still on. System not charging and no battery power at all and truck actually died from no power.
Jump started. Charging fine, no light!!!!!!!!! Truck never gave me another problem all day.

WTF is going on???? Anybody got any ideas?
I have heard that something in the computer actually tells the alternator to charge or not charge? Any truth to that?
I am stumped

 

Look for a loose connection at the alternator. Unplug the plug and check if carefully. See if the connectors are spread open a little bit and not making contact to the terminals in the alternator.

 

I would guess that this is kind of like the 'exciter' wire for the alternator?
I will check that as well.

 

Ever since Sunday morning, I haven't had a problem at all.
Haven't seen the charging light on the dash at all.
Got in it this morning and it barely started.