A California motor vehicle bill of sale is part of the vehicle registration process. Use a free template to write your own bill of sale.Mail to Department of Motor Vehicles, P.O. Box 942859, Sacramento, CA 94259. Be sure this form is filled out completely and correctly. The California bill of sale form, REG 135, allows a buyer to purchase a motorized vehicle or vessel in the State. All fields should be filled-in on the form.