Open the chart of accounts and create a new ...
fixed asset account, as a sub account of fixed assets and name it for the vehicle
another fixed asset account as a sub account of the vehicle fixed asset account and name it accum depreciation vehicle
use the vehicle fixed asset account as the expense (reason) for the purchase
End of the year you will do a journal entry for accumulated depreciation
debit depreciation expense, credit fixed asset accum deprec vehicle
see IRS pub 946 for depreciation schedules
