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One of the more exciting upgrades you can perform on your BMW is installing and upgrading your lamps to a high-intensity discharge (HID) system. This type of lighting system uses xenon bulbs, or, under the Bosch brand name, Litronic bulbs. The lamps use electric current that runs through a xenon gas mixture to create light, not unlike the operation of an ordinary fluorescent light bulb. In order to get the lamps working, however, the gas mixture must be subjected to an initial voltage of about 28,000 volts. Two small ballast units create this high voltage when starting the lamps and then taper it down to about 40 volts to keep the light on. The Hella units used in this particular project have a built-in safety circuit to prevent the 28,000 volts from being discharged if there are any disruptions or anomalies in the circuit.
Replacement bulbs tend to be very expensive, at about $100 each. I expect the cost to decrease, though, as more and more cars come equipped with this technology as stock equipment. The good news is that, unlike traditional halogen bulbs, the HID bulbs do not often burn out since they have no internal mechanical components and actually run very cool (like a normal fluorescent light bulb).
The lamp kits typically use 35-watt bulbs, which means that they draw about 2 to 3 amps of current after the initial startup. It's not uncommon for the ballast units to draw about 15 amps for less than a second as they are starting up the bulbs. The actual startup phase is typically less than a second--barely a noticeable difference from the stock configuration. With a halogen lamp system, a large portion of the energy spent in the system goes toward excess heat given off by the bulb. The HID systems are much more efficient. For example, a typical HID 35-watt bulb is about three times as bright as a 100-watt halogen bulb.
Thankfully, the installation is not difficult. It simply requires that you mount the ballast, integrate the bulbs into your housing, and wire up the system. HID systems only work well with the European ellipsoid headlamp housings (see Project 94). As of yet, I have never seen an HID kit installed in stock U.S.-spec headlamps. I'm sure it's possible, but the European headlamps make the task much simpler and will also disperse the light from the bulb in the proper fashion.
The European headlamps have large plastic covers on the rear that need to be slightly modified. Most of the HID kits available have a wire harness that has a large grommet on it. You need to take a small holesaw or Dremel tool and cut a hole in the rear of your plastic housing for the grommet to fit. Two wires are connected to the HID bulb; the other two tap into the connections for the old halogen bulb and power the relay located in the wire harness.
The HID system uses electrical current drawn off the battery and controlled by a relay. The harness included with the HID kit powers the relay with the current that formerly powered the original bulb. (See Photo 2 for a schematic of the system for further details.)
Mounting of the ballast can be a bit tricky, though. Component locations have changed quite a bit over the years. Just find a safe, secure spot near your headlamps and use the double-sided sticky tape or mounting brackets included with the HID kits (see Photo 3).You can also install an HID kit for your low beams, high beams, and even fog lamps. I have seen cars with three kits installed and their fog lamp switch modified so that all three are on at the same time.
When you're finished with the installation, be sure to align your headlamps so that the beams are not pointing into oncoming traffic. In most states, the use of nonfactory HID kits is designated for off-road use only. Keep in mind that if you don't have a street-legal headlamp system, you may invite tickets from law enforcement.
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Shown here is a typical HID conversion kit for European ellipsoid headlamps. A: Bracket for mounting the ballast. B: Hella-manufactured ballast unit. C: Battery ground connection. D: Battery positive lead connection. E/F: H4 connector (taps into the car's original lamp harness and reroutes power to the relay). G: Plugs that tap into the original lamp connector. H/I: Plug to provide power to the ballast unit. J/K: High-voltage wires that supply the bulb. L: HID bulb. M: High-voltage wire harness. N: Inline fuse. O: Relay.
Most of the HID kits I have seen include hard-to-read wiring diagrams, so I created this easy-to-follow schematic. The voltage from the battery supplies the HID ballast unit, and its on/off function is controlled by the relay integrated into the harness. This connection is also protected by an inline fuse. The relay that triggers power flow to the ballast is powered by the voltage from the original H4 plug located inside the headlamp housing. Because of this wiring arrangement, the relay is powered on (and turns on the HID system) when voltage is applied to the plug where the old H4 bulb was located.
Shown here are two potential mounting places for the HID ballast units. Although not ideal, attaching it with Velcro to the washer bottle does allow easy access. I would follow up with long zip ties to secure the unit to the bottle. The right-hand-side ballast is attached underneath the front support bar with zip ties and Velcro.