The Ole’ Rust Bucket quest asks you to find missing parts for the old Truck — 4 wheels and 1 headlight. These are scattered all over your farm and you can dig them up by harvesting your crops as usual.
Open the quest and click “Start Quest” so you can start picking up the wheels you may have already noticed lying around.
When you see a part, click on it to pick it up.
After you find all the missing items, install them by clicking on the broken Truck (or the quest menu).