Driving along yesterday and pull upto a stop. The check gages light comes on and rings that charming belltone.
Volts are low. Accelerate from stop and volts come up....a little...enough to clear the check gages light.
Volts continue to drop and I'm headed for the parts store.
Of course, they find the battery voltage low but, one battery has a dead cell. They are four years old so I say "Replace them".
Voltage is back up to >13V so I go on my merry way to Fla.
Get up this morning, clean terminals and connections a little better and fire it up.
Volts come up to 14V.
Great.
Head to Tampa to drop the load on the trailer.
On the way back, volts start to drop...and drop...and then the gages drop in and out and the truck quits.
"Well, maybe the alternator was bad after all."
Nope.
Disconnected the batteries so I could put my winch batteries in to get home.
Batteries are at 12.57 Volts.
Hmmm. Hook them back up and they are between 8-9 volts.
I'm guessing the problem is a short in the PCM....?
Disconnected the ECM power and the pigtail from the Power center to the ECM (The one on the block) and still the batteries drop to 8-9 volts when you hook them back up.

This is on a 98.5 2500 with a 5 speed.

Any healp is greatly appreciated.

 

so u replaced the alternator?

 

NO.
Something appears to be shorting the batteries to ground.
They are close to a full charge(about 12.5), but when you hook them up (Key off) they only read 8-9 volts.

 

with the truck shut off, and the batteries connected, feel the alternator. If it is warm or hot to the touch, your problem is within the alternator, if not, look for the hot spot, your ground issue will be very close by.

 

Truck is home.
Alternator, grid heaters and ECM disconnected.
Pulled all the fuses from the power center/fuse box under the hood.
Still have a ground.
Time to start looking.
Wish I had my infrared thermometer here.
Finding the hot spot would be easy then.

 

Okay, ever seen an alternator go bad....but not?
I didn't have an intermittant short.
I had an intermittant charging issue.
Took the alternator off and ran multiple spins at the parts store.
Got to see it fail and replaced it.
The gages don't lie, but sometimes they confuse the heck out of ya'.

Thanks for all the input.

 

just replace the alternator. mine did roughly the same thing in feb. if your unsure, take it off, run up to the auto parts store, and have it checked. within a couple days i couldnt even get the truck to run because the alternator wasnt putting out enough juice to work the electronics.

 

Done.
Back in GA and happy...just poorer.