1975 GMC K15 with System Mount Switch;. 1976 GMC K15 with System Mount Switch;. 1977 GMC K15 Submodel: Base; Engine: 4.1L L6; EngineVIN: D; FuelSystem: 1BBL; with System Mount Switch;. 1977 GMC K15 Submodel: Base; Engine: 5.7L V8; EngineVIN: L; FuelSystem: 4BBL; with System Mount Switch;.
