I had to to convert from 5 years macrs to straight line depreciation on a truck over 6000 lbs. Say on the fourth year of depreciation, if the truck your bought was $10,000 and the 4th year was 10% business use which is $1,000 and your prior accumulative depreciation was say $4000.  Is  your depreciation deduction for the current year is 0 because your accumulative depreciation $4,000 is greater than $1,000 business basis?