It depends. Did you have a loss on a truck because you sold it at a loss, or because it was damaged or stolen?
If the truck is a personal use truck, no deduction is allowed for selling it at a loss. In addition, there is no longer a deduction for casualty losses on Schedule A for the Federal return for personal property unless the loss was due to a Federally declared disaster.
If the truck was used in a Schedule C business, then you would report its sale, or its loss due to a casualty.