What if I paid for car registration for a car registered under my mother's name?

If your Mom owns the vehicle, then no you may not deduct it.

If any portion of the fee is deductible it is deducted by the individual that owned the car and paid the fee.

I hope this answers your question.

What if a car is co-owned by my parents and me, both on registration and title, but they pay the registration, car payments, and insurance -- I pay gas and maintenance, but I am the only driver and use the car for my business, may I deduct all those expenses on my schedule C?

No, you can only deduct the expenses that you paid. But you can deduct the expenses for operating the car for your business. 

 

Vehicle expenses can be reported by actual expenses, gas, and maintenance; or using the mileage method. This is a rate that you multiply the total miles driven. 

 

Please see this TurboTax Tips for more information about Standard Mileage vs. Actual Expenses.

 

@TaxTN99