The tax law that lets donors of vehicles to charity claim the fair market value will change January 1. Under the American Jobs Creation Act of 2004 signed into law Oct. 22, claims of $500 or more for donated cars, boats and planes will be limited to what the donated item sells for at auction, not a theoretical assessment, which is much higher. In order to take a deduction, a written statement of the sales proceeds will be required, as of the New Year, to be obtained and attached to your tax return. For those that know the difference between Kelley Blue Book wholesale value and suggested retail value, that´s a lot less tax relief.