I have 99' Pontiac Bonneville 3.8L 'K'(no supercharger.)
One day, it is running fine for about 40 minutes with no electrical
symptoms. I shut it off, after about 20 minutes I get back in my car
and nothing. The gauges, radio, and lights worked and looked normal
and bright. I get a jump from a passerby, the car starts fine. I took
it to my local "Advance Auto Parts Store" they test the battery on the
car and it passed. I started the car and pulled the pos cable off the
battery --the car stalled instantly. I took the alternator out of the
car and had it bench tested --it passed.
By the way, my serpentine belt is less than a year old with about 20k
miles on it. I am driving my wife's car until I figure this out. No
need to be stranded on the interstate.
Any ideas? Could it be the battery, starter, or alternator?