To enter interest on an automobile loan for business expenses that you didn't record as automobile expense (you must be signed into your return for this link to work) in TurboTax follow the steps below
Log in to TurboTax.
Navigate to Federal Taxes.
Go to Deductions.
Select Business Expenses.
Choose Common Business Expenses.
Enter Interest Expense: If you paid or incurred interest in the course of your trade or business activities that you have not claimed elsewhere on this return, enter that amount.