67 Pa. Code § 171.84
Equipment added and alterations made to a school bus after its manufacture shall meet applicable Federal test standards. Additional equipment items not specifically required by Federal standards, 75 Pa.C.S. §§ 101-9821 (relating to the Vehicle Code) or Department-promulgated regulations for vehicles, equipment and devices installed on or in a school bus shall bear the trademark, name or code symbol under which it is approved. Installed additional equipment may not interfere with or violate any equipment standard or requirement. Equipment items not specifically required by law or regulation may not replace or interfere with a required equipment item.
67 Pa. Code § 171.84
The provisions of this §171.84 issued under the Vehicle Code, 75 Pa.C.S. §§ 4103, 4551-4553 and 6103.