To record the entry for the purchase of a vehicle you will need two things, your vehicle purchase contract and your loan documents.

GL accounts used:

Fixed Assets (Transportation Equip or Vehicles) - Debit
Note Payable (Setup a new GL for each Note you owe) - Credit
If there was a down payment - Cash in Bank - Credit
If there was a trade - Fixed Assets (Transportation Equip or Vehicles) - Credit

Here is an example with all of the above involved:

The company traded a used truck for a brand new one - 
 

Sale Price: $44918.82

Rebate: $6,043.20
=  $38875.62

Trade Value Given - $3000

Cash  Down - $5000

Financed Amount - $30875.62