My handle on this forum reveals what I do for a living.
Tax credits fall into two buckets: Personal credits and business credits. The gurus upstream do not appear to know anything at all about business credits, so if you wish to heed their advice by all means go for it. But you get what you pay for.
The personal credit under IRC Section 30D is not limited by the Alternative Minimum Tax. It is only limited by the income tax on the taxpayer's 1040.
However, business credits have a much more complicated structure. First they are limited to the business income derived from said business and the taxes thereon on form 1040 or 1120. Second, business credits do not receive the favorable treatment for Alternative Minimum Tax. These business credits can reduce regular income tax, but not below AMT. Your tax return will include form 3800, General Business Credits as part of your filing package. So, your tax adviser is correct. You are not receiving the full $7,500 tax credit this year because either the profit from your S Corp was not large enough or the credit reduces your income tax below AMT.
However, the good news is that for those who take the Section 30D as a business credit, any unused credit is carried forward up to twenty years.
I am shocked that all the experts on this forum did not explain this to you correctly.
You could have saved a lot of sophistry if you had told us who owns the car and how your personal income taxes are structured when you started this thread.
Finally, to those sainted individuals who are blasted this person's CPA for being stupid, lazy or whatever, I think you owe this person an apology. You are the ones who are wrong.