Complex sentence: Oldsmar, being right on the county line between Pinellas and Hillsborough stayed 813 despite being in Pinellas because its trunk was wired into the Tampa line and it would have cost too much to rewire it.
Split into simpler sentences: Oldsmar, being right on the Pinellas/Hillsborough line, stayed 813 despite being in Pinellas. Oldsmar's trunk was wired into the Tampa line and it would have cost too much to rewire it.