Quote - The object has many materials - you're not looking at the one for the box. Look at your last screen shot - it says Material: hull.

Yeah I said that was an example of what the main ship looked like with image map nodes.  I was expecting something like that for the cargo box.

Quote - While you're in the material room, find your box in the preview window and click it with your mouse. The material that controls whatever you clicked on will become the active material in the material editor. You should then be able to figure out how to switch the image.

A-ha!  This was very helpful.  In the "Material" dropdown, I didn't have 'car1' selected.  Problem solved!