If you are referring to your new vehicle for personal use, you can only deduct sales tax you pay, you cannot deduct the loan interest. You can only deduct car loan interest if it's for business use.
To enter sales tax paid in TurboTax online program, please follow these steps:
1. After sign in and select Take me to my return
2. At the right upper corner, in the search box, type in sales tax then Enter
3. Select Jump to sales tax
4. On screen, Let's Compare Your Sales Tax and Income Tax - select Try Sales Deduction Anyway
5. On screen, How do you want to enter your sales tax info? , select EasyGuide and follow the prompts.