It protects the switches from high currents, namely HID bulbs, they may consume less wattage, ie 35W or so for OEM applications, but they startup with a large amount power.
"When you open a switch that has current going through it there is a spark. The spark damages the contact points of the switch. The size of the spark and the damage caused is proportional to the amount of power going through the switch. The switches will fail sooner than they would otherwise. The relays are designed for high load, and are easily replaceable in the very rare circumstance that they fail. They're made by Bosch, so failure is unlikely."
From:
http://www.mahonkin.com/~milktree/he...relay-harness/
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2007 Toyota Camry SE 2GR-FE
Retrofit TSX HID Projectors | TRD Lowering Springs | Smoked LED Tails | Custom Apexi WS2 Catback Exhaust | BlueBatMobile Eyelids| UR Front Strut Bar | UR 23mm Rear Sway Bar | K&N Short Ram Intake| Kenwood DNX8120 In-dash | Lexus IS350 18" Wheels | Toyota Japan JDM Vent Visors | IS-F Black Leather Shift Knob
Other cars: F20C (AP1) | 2JZ-GE (JCE10)
