If you hold the owner's truck without his permission, you are committing theft--you could find yourself in jail. (It's not just "any" theft--it would be a felony, since it's a motor vehicle.) Your employer could also sue you for the truck's value if anything happens to it while you have it.If you have not been paid, the correct way to seek your money is to sue the owner in a court of law. If you can prove that you did the work and what you should have been paid, you should win. Once you have a court judgment in your favor, then there are a variety of legal mechanisms you could use to collect if still not paid--including at that time, potentially having a court officer seize the truck.For $7,000, you'd be well advised to retain an attorney to represent you, though you could represent yourself if you don't want or can't afford a lawyer. (If the amount is less than the maximum threshhold for your small claims court, you could sue in small claims, which is easier for people representing themselves.)