the amount of the credit depends on the vehicle. the maximum that can be used depends on line 18 of the 1040 reduced by certain personal credits.
the following is only a guess because we lack information about your taxes such as other tax credits and whether you itemize or take the standard deduction. many other factors can also affect your tax liability that is eligible for offset by the EV credit. also, different rules would apply if this was a tax credit for business use of the vehicle. see IRS form 8936 and instructions.
if the $70K is your adjusted gross income then with the standard deduction your taxable income would be about $44K. the tax on that is only about $4900 and this would have to be reduced by certain personal credits. To get to a tax liability of $7,500 before personal credits your AGI with the standard deduction would need to go up by about $22K.
in other words, it takes about $66K in taxable income (MFJ) to produce a $7500 tax liability and that's before any reduction for certain personal tax credits (form 8936 line 21)
