In my opinion, I would approach this in two different ways:

1)  Do not show the rest of the "wizard" until the first two selections are made.  Allow the user to only focus on the initial model selection before they concern themselves with exterior, interior, etc.

2)  Change the visual design to make this appear more like a wizard.  A wizard sometimes entails a linear or logical path of actions.  The visual style of this wizard appears more like a horizontal navigation, which makes the selection confusing.

These are two drastic changes, and may require more time you want to invest, but I think it may lead to a less confusing interface (less available clicks, less selections, more structure).