§ 420. Guaranties to sellers of liabilities of buyers under retail
instalment contracts. (a) No guaranty given to the seller or to the
seller and the seller's assignee of the liabilities of a buyer under a
retail instalment contract shall be valid unless the guaranty is
incorporated in or endorsed on the contract or identifies the contract
and specifies the time balance thereof. A copy of the guaranty and the
contract to which it relates shall be given or mailed to the guarantor
upon or immediately after the execution and delivery of the guaranty by
the guarantor. As used in this section, "retail instalment contract" and
"contract" include a retail instalment obligation and a retail
instalment contract as defined in the motor vehicle retail instalment
sales act, constituting article nine of this chapter. This section does
not apply to a guaranty made by a seller or a holder of a retail
instalment contract.

(b) No guaranty given to the seller or to the seller and the seller's
assignee of the liabilities of a buyer under a retail instalment
contract shall relate to any future retail instalment contracts.