my son has a 2002 tl and is having a problem. Sometimes when driving the battery light comes on then after a few minutes all the other dummy lights then all lights and guages die then car has almost no power. The first time this happened he was on his way home and just wanted to make it to a safe spot to stop. Anyway he shut car off and waited for me. When i got there the car started right up and ran fine to make it the 8ish miles home.
the car sat for a couple weeks at his house and when i tested battery voltage was a bit low (12.04v) but car would start. 14.2 volts when running. I brought the battery to auto zone to have it tested and it had a bad cell. Battery was replaced at this point. Problem happeed again so I brought my meter to his house the next day. Battery at 12.6v and 14v when running. Today i was with him and car acted up again (first time i have seen it first hand. This time we left the car running and it was at 7v not a typo when i shut off car voltage slowly rose up.
Does this sound like a intermittent alternator problem or a short somewhere? All voltages were taken at battery, tomorrow i will test voltage at the alternator and see what the results are. The hard part is sometimes everything is fine and other times obviously not so. It is difficult when i cant always get the same results

Today i tested the voltage directly at alternator and was pushing around 10 volts with only engine running so i am going to go ahead and say alternator is shot. I have never had one work fine sometimes( 14.2 ) v and not work at others but there is a first time for everything I guess