Alternator Issue?

I have a 2004 Tundra SR5 with a 4.7L engine with 227k miles. Went for a ride yesterday. Aside from the cold temperature 20F outside, all seemed fine until the battery light illuminated while I was driving. Went home and threw a voltmeter on the battery posts and it was reading low at 11.8v while the engine was idling. I figured it time for a new alternator. Went out this morning and started the Tundra and noticed the battery light was no longer illuminated and the voltage meter on dash was withing the acceptable range but more toward the lower end. I had to shut down the motor and restarted after a minute and the battery light came on but shut off after about 3 minutes of idling. Again I checked the voltage at the battery posts and it's still at 11.8v. I'm fairly certain the alternator is at fault (it's probably the original) but is there any fuse or relay that could be causing the issue? Also why wouldn't the battery light stay lit if the voltage is so low? Thanks.

 

I had similar recent issues with my 2005. If it is intermittent like this, you need to look for potential grounding issues coming off the alternator or the battery. Ultimately my issue was the lead coming off the battery going to the 140amp alternator fuse had poor connectivity because the feet on the feet were partially fried, but it did not actual break the fuse. Sometimes it would be fine, sometimes the connectivity was poor, resulting in battery light sometimes, and absolutely fine the other times. As a side note, getting to the 140amp fuse is a bitch so I would check all other items first.

Here is the post where I went through it recently.... https://www.tundras.com/threads/charging-alternator-problems.97131/#post-2466483

Also, there are videos on youtube on how to test for voltage drop (which would indicate bad ground).