2010 Tundra 5.7 - charging system problem

2010 Tundra 5.7 with tow package

I've been dealing with a charging system issue for 5 months now.

It will stop charging while driving. The battery light does NOT turn on when this happens.
Voltmeter just drops to about 12V and declines as the battery slowly goes dead.
If you turn off the truck and then turn the key to the run position the battery light does NOT turn on.

If the truck is cold and you turn the key to the run position the battery light DOES turn on.

Sometimes while driving the volt gauge will jump up and down from battery level to charge level. Occasionally the battery light will flicker while this happens.

I have replaced the alternator ( that's a nightmare). Did not improve the situation.
I had the replacement alternator tested before installing.

I have also replaced the following fuses : ALT-S, MET-B, MET, LH-IG. Did not improve the situation.

I've also swapped batteries. Again did not help.

It seems like the clue is the battery light NOT turning on.

As the weather has turned colder it takes a lot longer for charging to stop. Some trips it does not act up at all.

So it seems to be temperature related and is probably in the engine compartment and not in the cabin?

Anybody have any ideas?
I've run out of things to try.

 

Nope no aftermarket additions or modifications.

 

Battery is dead.. swap it out.. I had a yellow top, Optima, and would do similar things ni battery light, just dancing... I replaced it 4 years and replaced that one anyway ago with weeks of warranty to spare..

 

I have already tried swapping batteries, problem does not go away.

 

Have you checked the connections at the alternator, may be a bad main ground? Swapping the alternator wouldn't address a bad ground on the body-side. Odd issue, hope you get it sorted.

 

Sounds like a bad ground. You need to poke around with a multimeter when it's happening. I would check alt voltage vs battery voltage. Also resistance between alt case and neg battery terminal should be zero.

 

Start the truck and unhook the battery. If it stays running the alternator wires should be okay. Check the bridge between the alt and battery for wear and corrosion.

 

Don't do this please. It's not a good idea on a modern car. You can fry electronics like the ecu, tcu, and bcm. Use a multimeter like I suggested. Much safer.

 

Checked the connections on the alternator, all good. Re-cleaned the battery connections. Measured the voltage drop from alternator to main busbar fuse with engine running and it's only about 0.07V drop, so that should be ok. No difference if measuring voltage at main busbar fuse or at battery, so the bridge wire and battery + connection is good. I still need to check ground resistance from batter - to alternator case.

I'll have to try to recheck all of these once I get it to act up again.

 

This is the right way to do this. Let us know what the problem ends up being.