Can I add my car I am currently paying on as a major purchase for a tax deduction?

Yes, you can claim a deduction for any sales tax paid on your new vehicle. Here's how to enter the sales tax you paid during 2019:

1. With your tax return open in TurboTax, search for sales tax and then select the Jump to link in the search results.
2. On the Sales Tax and Income Tax screen, select Continue with Sales Tax.
   • In the CD/download software, the screen name will be Let's Compare Your Sales Tax and Income Tax – click Try Sales Tax.
3. When asked how you want to enter your sales tax, select EasyGuide.
4. Answer the questions on the next few screens. When you get to the Major Purchases screen, answer Yes.
5. Follow the on-screen instructions to enter your info.

You only deduct the sales tax you actually paid in 2019.  However this includes sales tax you paid with a loan, because--since you promised to repay the loan--paying with a loan is treated the same as paying with cash for determining the deduction value.  (If you failed to repay the loan that's a different story later down the road.)