A driver's license is required to operate an ATV in California if the rider is over the age of 18.
Homemade trailer exceeding 3,000 pounds, are required to go through the rebuilt application process and inspection. Homemade trailers 3,000 pounds or less may request an assigned serial number from their county treasurer to begin the title application process.
Get a moving permit from DMV, take it to DMV or your local Highway Patrol office and they will inspect it. It needs a serial number or VIN and if it doesn't have one, they will assign one. Then you go to DMV after it is 'verified' and register it.
To register a specially constructed vehicle (including a kit commercial vehicle), you will need: A completed Application for Title or Registration (REG 343) form. A vehicle verification by an authorized DMV employee. Bring your vehicle to a DMV office for verification.
1.155 Vehicles Exempt from Registration Aircraft Refueling Vehicles (VC §4021) ... Cemetery Equipment (VC §§4012 and 5011) ... Disaster Relief Vehicles (VC §4005) ... Firefighting Equipment (VC §4015, CCR §157) ... Forklift Trucks (VC §4013) ... Golf Carts (VC §§345, 4019, 21115) ... Hauled Vehicles (VC §4009)