The radio turns off and dash lights dim, ABS light probably comes on as well, because they are not getting 12 volts any longer. The car is running off the battery and draining it. Then when it's that low the battery can't provide spark and the car dies.

Boosting it wouldn't work because with a dead battery and a dead alternator there won't be enough power to start it or anything to keep it running.

Anyways, the alternator needs to be replaced/rebuilt and recharge the battery. Hope the battery isn't too old, otherwise 2 drains may have killed it for good.

I want to say it is caused by bad diodes but I don't know for sure what causes them to charge intermittently when they go bad.

Where abouts in Ontario are you? I am in Belleville/Kingston, I could help you out if you're close and need a hand.

Also, my parents Grand Prix had this same issue for about a week last winter. Then the alternator crapped out entirely and left them stranded.