I have a 05 TL 5AT w/navi. I noticed last night while driving that if I put to much of a load on the charging system, the car shuts down and comes right back on. I had the radio and headlights on, if I turned the fogs on the navigation would cut out and my head lights would dim. At one point my vsa, brake, check engine all came on. I shut it off, started it again, and it was back to normal. If I tried to roll up the window when it was already up, the car would completely shut down while driving. Gauge, interior and exterior lighting would all go dead like the car had no power what so ever.

It has a new battery in it from when I bought it. It seems like a alt issue or possibly a fuse box issue. I'm mechanically inclined enough and have a volt meter to do any test anyone throws at me. The alt is charging at 14v and battery is at 12v.

 

I have tried to recreate the issue today with no luck. I'll be trying again tonight as well. It seems intermittent, but would like resolved. Any suggestions are appreciated.

 

I think your alternator is starting to go bad.

 

They also have issues with positive battery cables going bad. They get corroded internally and cause high resistance. The alternator can sustain the vehicle, but it cannot keep up with large needs for amperage all the time. If the positive cable is bad, it will act just like the battery is not in the vehicle under a large load.