Fixed fast blinking tail light, now car keeps dying on 2004 Chevrolet Malibu Maxx

My car had service for oil change and brake work. My right driver side blinker bulb frequently works loose, and must be tightened by squeezing the metal grip that holds it in. They did that, too. The night I picked up my car, the stereo didn't work, and the digital read-out screen (clock, etc.) was really messed up. The next day, my car wouldn't start. It's now been 5 days. The car has been jumped 3 times, battery checks out fine, alternator tests at just under 13, then works its way up over 13 as the car runs. The shop doesn't find any stray current anywhere that would cause the battery to keep dying. I wonder if playing with the tail light messed things up, or if it's just a coincidence? Do I need a new alternator? I'm nervous every time I walk up to my car to start it. Thanks in advance for your advice.

Asked by for the 2004 Chevrolet Malibu Maxx
I doubt the taillight has anything to do with this. When does the car die, when driving or after it has been parked for awhile? Did the shop perform an alternator amperage output test? This test is to determine the maximum amperage output of the alternator and is an important test to determine if the alternator is capable of keeping the battery charged at all times. The battery and cables will also need to be properly tested.
2 answers
Seems like there are 2 unrelated issues here. The fast blinking turn signal light usually means one of the lights on that side of the vehicle is burned out or is not making contact. If the bulb is burned out, simply replace it. If it is a contact issue it is best to replace the light assembly rather than to try to fix it. The car dying issue could be due to any number of issues but it's highly unlikely the turn signal issue is one of them. You'll need to have service facility diagnose the problem. I had a similar problem 2X and in both cases a re-flash of the main board fixed it. The cost for that was $90 each time (outrageous) at the dealer but the dealer is the only place that can do that.