One of the headlights on our '93 Saab 9-5 has burned out. It uses Xenon bulbs, which are rather pricey. I’ve already ordered a replacement from the local auto parts store, but I’m a little concerned about two things:
The owner’s manual says that these lamps should only be replaced by the dealer. The warning is accompanied by attention-grabbing colors and exclamation points. However, the replacement doesn’t seem that difficult. I understand that these things use high-voltage AC power, and I’m assuming that the warning is due to an overabundance of caution on the part of the manufacturer for that reason. I’ll disconnect the battery before replacing the bulb – do I need to worry about anything else?
Also, I’ve seen recommendations that both lamps be replaced at the same time, but none of the sources for this recommendation supplied any reason. Some speculated that there might be minor differences in the color of the lamps if they weren’t replaced simultaneously, but this doesn’t concern me much. Did I mention that these things are pricey? Do I really need to replace both lamps?
As far as I can tell the only reason why you’re supposed to replace them in pairs is that if one went out, the other one theoretically won’t be far behind.
The important thing to keep in mind when you’re changing them yourself if to make sure you don’t touch the actual bulb part because the oils on your skin will cook and ruin the bulb. On some cars, this can be very tricky-- you might want to practice putting the old one back in before you risk that expensive new bulb.
You may well lose your radio presets, and may have to re-enter a PIN in order for the radio to even work if you disconnect the battery. Check your owners manual.
I’m not sure if there is a capacitor involved in the circuit at all, but since they are high voltage there might be. After disconnecting the battery, turn the headlights on briefly, high and low beams, to make sure all of the voltage is drained from the system. It will only take a second and is better than getting shocked.
Of course, if there are separate capacitors for each bulb, even following the above procedure could get you a little jolt. So I’d be careful not to touch the conductors when changing the bulb.
The HV is used only to start the bulb. After that, the arc is self-sustaining and requires only around 12 VDC to run. The HV trigger circuit is similar to that found in photoflashes (with good reason, since flash tubes are also a type of xenon arc lamp)–it’s high voltage but low current from a high impedance. It’ll give you a nice knock, but it’s about as lethal as piezo burner igniter.