Instructions
Drive or walk to Mumbo Motors if you are in the hub world of Showdown Town. If you are in one of the sub worlds just press "Start" to pause the game, and then select either "Build Vehicle" or "Change Vehicle" to be transported to Mumbo Motors.
Use the left control stick to switch between "Workshop," "Vehicle Database," "Paint Shop" and "Test-O-Track." "Workshop" is where you will do most of the mechanic work, while you can give your vehicle a new color in "Paint Shop." You can load and switch between your creations in "Vehicle Database" and try them out in the "Test-O-Track."
Press "A" and scroll down the parts list while in "Workshop" to view the available parts for your vehicles.
Place a part on your creation by moving it to the proper location with the left control stick, and then press "A."
Modify your vehicle by pressing "X." You can then select a part and move or delete it. Use the "Y" button to delete parts.
Save the vehicle by going to "Vehicle Database" and choosing that option.
Scroll over to "Exit Garage" and press "A" to return to the game.