Adding HID lights:

HID lights are, essentially, fluorescent lights. This makes them fairly efficient in terms of light for power used, but they require high frequency, high-voltage AC current to work, and your car's electrical system is a low-voltage DC system. So, this means an additional transformer is required, which takes up space and robs you of some of the efficiency by disappating some of the energy as heat rather than light. A typical HID light uses 35W of power to produce about 4x the light a normal 55W headlight bulb produces. The current draw from the transformer, however, raises this to about 80W for both front bulbs, which is still better than 110W for two non-HID bulbs.

However, when an HID bulb is turned on, a high current is required to get them started, about 200W per bulb for the first few seconds of operation. This is nearly 4x the current required to run regular bulbs, so the stock wiring harness is NOT adequate to power these lights. You need to run 30amp relays (one per bulb) and 20amp fuses (one per bulb) and heavy gauge wire (14g is just adequate, 12g would be better) from the relay to the battery and the relay to the bulbs to power them. Use the normal headlight wires to switch the relays.

If you do not do this, you're certainly going to blow fuses, and you may burn up the stock headlight switch, which is very expensive and hard to find.