I recently purchased two replacement light fixtures for out bathroom and hallway. The boxes each had a warning stating, "Warning! Risk of fire. Most houses built before 1985 have wires rated at 60 degress C. This fixture is rated at 90 degrees C. Consult a qualified electrician before installation." I don't really want to burn the house down. What are they talking about, and if my house has the old wiring, how can I identify it, and what kind of fixture should I buy?