Mich. Comp. Laws § 492.113a

Sec. 13a. (1) A seller in an installment sale transaction may pay on behalf of the buyer and agree to finance in the installment sale contract all or part of the balance of any indebtedness secured by a motor vehicle that the seller takes in trade in the installment sale transaction or all or any part of the balance owed under a lease of a motor vehicle that is terminated in connection with the installment sale transaction. (2) If subsection (1) applies in an installment sale transaction, then the other necessary or incidental costs included in the installment sale contract under section 13(2)(e) shall include the amount the seller agreed to finance under subsection (1).