Went to start my truck the other morning and it was stone dead, lights would not even come on. I put the battery charger on it for about a 1/2 hr and it started, Volt gauge indicated it was only charging around 11.5 volts.

I needed to run an errand so I used the truck to go to town and after about 10-15 minutes volt gauge indicated 14.5 volts. When I got home I shut it down and waited a couple of minutes and it restarted but only showed 11.5 volts again. I let it run for another 10 minutes or so and once again it started to work its way back to 14.5 volts.

I went out this morning and the truck is dead again. Grid heaters appear to cycle and shut off so I don`t think they are the issue. Could this indicate a bad diode in the alt??? Batterys are less than a year old. Thanks for the help.

 

Sounds like the alternator. Charge the batteries overnight and then run to an autoparts store of your choice AutoZone, Advance, etc and they will check your batteries and alternator for free.

 

sounds like bad battery, they may be loosing charge and when you start it at first it is low and the alt. is working and charging them up. need to load test the batteries. My truck will take a while for the alt. to show full voltage output and so does my boys. ED

 

You can tap a metal screwdriver on the back of the alternator with the truck running (if you dare) and if it is magnetized the alternator is charging. Best bet is to go to AutoZone and have them check the batteries. Just remember to separate them from one another or you won't get a good reading....

 

I'd confirm that the grids are not sticking on!!, easy to do just unhook the smaller wire from the positive battery post on the drv side, the smaller wires go down to the grid relay. leave the wire off, drive truck and see if your batterys hold their charge and your volt gauges shows charging

when truck is running alternator can barely keep up if the grids are sucking batterys dead.
also easy to test, unhook wire as explained above. with truck engine off, touch the wire back on to the positive terminal, if there is a spark the relays are stuck on.

If you pass the above test, and have eliminsated the grids as a culprit, remove alt and have it tested and have batterys load tested to confirm their condition

 

Had the same problem! Turned out it was a short in my wiring!

 

Well I ended up having to take a chance and drive the truck 350 miles on Saturday, since then the batteries have not gone dead. What did happen is I lost a couple of functions to my overhead computer. Specifically, the function that shows the real time fuel milage, however the average fuel milage still works.. No idea what the heck is going on there.

I did check the grid heaters, they do not seem to be drawing anything as confirmed when I reconnect the small wire on the battery. However, every time I shut the truck off and went to restart it, the gauge would only show 12.5 volts or so, then slowly it would climb back to 14.5 when running down the road. When I would stop for a light the gauge would drop to somewhere around 13.8 volts. I`m thinking I have a bad battery. Hopefully this weekend I will get a chance to load test them.

 

I had the same problem even with brand new red top optima batteries. They would die on me before I could even finish putting the terminal leads on them. I replaced the alternator and that didn't help either. Then I realized my intake manifold had gotten really dark in color and that's when it occurred to me to check the grid heater and the grid heater relay. I check the relay with a mulitmeter and the contacts were closed shut. I replace it and now I have no problems

 

Charge them, then leave them disconnected over night.
Try one at a time in the morning to start.

 

Mine was a bad battery. Replaced them both and no moe dead batteries.

 

If the heaters are staying on your volt gauge will lean well to the left all the time.

Mine points to the right after warm up during average speeds.

How are you getting 12.5, 14.5 and 13.8 readings?

The factory gauge is not very accurate, BTW, just gives an average range....