S.C. Code Ann. § 37-2-409

(1) If debts arising from two or more consumer credit sales, other than sales pursuant to a revolving charge account, are secured by cross-collateral (Section 37-2-408) or consolidated into one debt payable on a single schedule of payments, and the debt is secured by security interests taken with respect to one or more of the sales, payments received by the seller after the taking of the cross-collateral or the consolidation are deemed, for the purpose of determining the amount of the debt secured by the various security interests, to have been applied pro rata to the payment of the debts arising from the sales. Proration shall be computed on the original debts secured by the various security interests. To the extent debts are paid according to this section, security interests in items of property terminate as the debts originally incurred with respect to each item are paid. (2) Payments received by the seller upon a revolving charge account are deemed, for the purpose of determining the amount of the debt secured by the various security interests, to have been applied first to the payment of credit service charges in the order of their entry to the account and then to the payment of debts in the order in which the entries to the account showing the debts were made. (3) If the debts consolidated arose from two or more sales made on the same day, payments received by the seller are deemed for the purpose of determining the amount of the debt secured by the various security interests, to have been applied first to the payment of the smallest debt.