There is no IRS form 8660. Did you mean IRS Form 8606: Nondeductible IRAs?
You may need to amend your 2017 income tax return to generate form 8606. Please read the information below.
We'll automatically generate and fill out Form 8606 (Nondeductible IRAs) if you reported any of these on your tax return:
However, if any of these 3 situations apply to you:
To trigger the 8606 in TurboTax:
For the 4 situations listed at the top of this article, you can trigger Form 8606 with these instructions:
Tip: On joint returns, 8606-T stands for "taxpayer" (first person listed on the return) and 8606-S denotes "spouse."
There has never been any bug that prevents you from being able to enter your year-end balance in traditional IRAs. Click the continue button on the Your 1099-R Entries page to reach the question that asks for this. (However, if you have entered no Forms 1099-R reporting a distribution or Roth conversion from a traditional IRA or have no basis in nondeductible traditional IRA contributions, TurboTax has no need to know your year-end balance in traditional IRAs for Form 8606.)