(a) General rule.--Where multiple policies apply, payment shall be made in the following order of priority:
(1) A policy covering a motor vehicle occupied by the injured person at the time of the accident.
(2) A policy covering a motor vehicle not involved in the accident with respect to which the injured person is an insured.
(b) Multiple sources of equal priority.--The insurer against whom a claim is asserted first under the priorities set forth in subsection (a) shall process and pay the claim as if wholly responsible. The insurer is thereafter entitled to recover contribution pro rata from any other insurer for the benefits paid and the costs of processing the claim.