322.21  Remaining balance on trade vehicle.
  The extension of credit by a retail seller to a retail buyer, pursuant to a retail installment contract, of the amount actually paid or to be paid by the retail seller to discharge a purchase-money security interest, as provided in section 554.9103, on a motor vehicle traded in by the retail buyer shall not subject the retail seller to the provisions of chapter 536 or 536A.
99 Acts, ch 13, §25; 2000 Acts, ch 1149, §167, 187