GM’s credit unit agreed to buy a mortgage group.

CoreStates Financial of Philadelphia said it had signed a definitive agreement to sell its Colonial Mortgage Service Group to General Motors Acceptance for $190 million. CoreStates said it would use the money to seek acquisitions. The deal would make the credit arm of General Motors the No. 2 mortgage-service company in the nation behind Lomas & Nettleton of Dallas, according to the Mortgage Bankers Assn. of America.