What If ?
If Doc Brown took a wrong turn heading to Twin Pines Mall, and broke down in front of the Ghostbusters firehouse.
Doc: can you store this top secret car in your firehouse?
Ray: sure we can. We'll make sure nothing happins to it.
3 weeks later. We call it the Time Buster.
Dont ask how the doors open. Even they dont know. They didnt think that far ahead.