Qualified Plug-in Electric Drive Motor Vehicle Credit

[3linkceo]

Does anyone know why changing the amount of mortgage interest that i am deducting on my schedule E for my rental property causes my Qualified Plug-in Electric Drive Motor Vehicle Credit to change? If i report the true amount of mortgage interest the $7500 credit i am eligible for only gives me about $2300. If I totally remove the mortgage interest it is giving me about $5500 of the $7500. I am not finding the correlation anywhere. This is supposed to be a 7500 deduction dollar for dollar to reduce my taxes owed i thought. i'm no where near 7500 in taxes owed, more like $10K so what am i not able to get the credit im eligible for and what the hell does my rental property have to do with this??