The credit is based on your tax liability, not withholding. Your tax liability is what the government keeps at the end of the year, after the tax is computed and all the withholding, deductions, credits, and refunds are taken into account. It is shown on line 22 of your tax return. (Income tax liability does not count self-employment tax or the various penalties for problems with IRAs, HSAs, and so on. The EV credit can't offset those taxes.)
Assuming your tax liability was $5000, if you want to use the full benefit of the credit, you need to find some way of increasing your taxable income so that you pay more tax. (Up to $2500 more tax, in your case. Generally, that would correspond to about $11,000 more of taxable income.)
Easy things would be to sell investments that have made a profit, like stocks. Do you have stocks with an $11,000 profit you could sell (not total value, just the gain over the purchase price?). However, be aware that if you like those stocks and want to keep owning them, you should wait 30 days before re-buying them.
Or you could convert a traditional pre-tax IRA or 401k to a Roth IRA or 401k, that will create taxable income. (You can convert just part of your account if your account is with more than $11,000. You don't have to convert the whole thing all at once.)
Or, if you are making pre-tax IRA or 401k contributions, change over to after-tax or Roth contributions until the end of the year, that will also create more taxable income. If you contributed to a pre-tax traditional IRA, you could recharacterize that as a Roth contribution, or convert it to a Roth IRA, to create more income tax that can be offset by the credit.
If you expect a bonus in January, could you persuade your employer to pay it in December?
