qdeezie

One thing I have not heard mentioned in this thread.

On the part of the block where the alternator bolts to, make sure you sand off that location or clean it up with a wire brush and put some electrical grease on it (the grease that goes on the battery posts - not to be confused with dielectric grease) so that the alternator has (and maintains) a proper ground.

Also, do the same thing to that same location on the alternator that bolts to the block.

That is something that LOTS of people overlook that I rarely hear mentioned. It truly does make a difference in the output of the alternator because it now has a solid ground that remains consistently solid due to the electrical grease being applied, which maintains the ground.

Dusty Crigger

If you get new alt and new battery and still have this problem you can narrow parasitic losses down to a group of items ans if you are lucky sometimes a specific item. Heres what I came up with, used it once and it worked but im not promising anything.
Full charge your battery, disconnect jumper cables, connect meter to battery then go to your fuse panel and pull fuse one. Go to your meter and see if you are loosing voltage. If its still draining at an undesired rate then put fuse back and go to number 2. Repeat until battery stops draining. If you pull a fuse and the drain rate noticably slow then anything that is on that fuse number could be your issue. Like I said this is something I came up with and it did work for me once before but maybe it was just pure luck.

05F1504x4

Well I Got a new battery yesterday and it cranked right up. Drove it 10 minutes. Cranked it up this morning and Drove It 5 mins to work. While I was sitting in the parking lot the battery light comes back on.. so alternator now?

digitaltrucker

Yep

Replace belt also.

05F1504x4

The brake light has been on and the ogometer lights up but doesnt display. But the guy that sold it to me said its been like that for over a year i didnt know if that would cause this issue.. waiting on my wife to bring my meter so i can check the battery.

Wesley416

Yeah See what reading you get for alternator output with a known good battery. Like another member said check grounds.

05F1504x4

With The new battery-

Reading volts while running with battery light on dash is 12.18
When i rev the gas the light goes off.

Battery reading with truck off is 12.48

I'm at work right now so I'll have to check the grounds on the radiator on my lunch

HeathMc

Not sure on the 12.8. My 2008 runs at 14.4. I have the tow package and if I'm not mistaken if you don't have the tow package it may run at different charging strategies.

qdeezie

How are the idler pullies? Do they spin freely? Remove the belt and make sure everything spins freely by hand. (Engine off of course.) PS Pump, water pump, etc. This is to make sure there is no drag causing it to undercharge.

05F1504x4

All belts and pulleys look good. Battery is still at 12ish. Looks like even though my alternator tested good it isn't
pushing the voltage on the battery to 14+ when running