I ran into a grammatical issue earlier today, and this problem has been bothering me the entire day, and evening... I cannot sleep. PLEASE HELP ME! Which one of the following is correct?

All the cars, except one is..

or

All the cars, except one are..

The reason I find this so difficult, is that "cars" is the subject, therefore it should be "are" (because, plural). But it sounds wrong, and therefore it should be "is"... but it can't be both of them. So which one is it?