Work In progress Picture stolen from Graeme86 I suspect most MK4 owners don't care about if there headlights can report bulb wattage to VCDS correctly, or what the OEM ballast options are, but if you are one of those people, then this is for you What's a Xenon? Xenon's/HID or more correctly Gas-discharge lamps generate light by doing exactly that. By creating a arc/discharge in a gas filled tube. The gas is usually Xenon, hence the name. 95% of vehicles use a standard 35 watt Xenon, but some, especially aftermarket, use a 55 watt bulb. The system in the Golf is a single projector for low beam, using a normal Halogen high beam. Newer systems are Bi-Xenon and these have a shutter which covers part of the bulb during normal operation. When high beam is activated the shutter lifts and the full bulb is exposed. (more on this later) What's a ballast? A ballast, apart from being heavy, is a old term used to describe the power supply and ignitor for the Xenon. You're probably more familiar with them from household florescent lamps. In the VW system, and many others, people refer to the silver box that is remote mounted or on the back of the headlight as "ballast". In reality this unit is just a 85 volt power supply used to sustain the arc. The actual arc striker is a separate device inside the lamp body, very close to the bulb connected using HV cable. This provides an initial 20,000 volt pulse to ionise the Xenon before letting the full current 85 volts pass to sustain the arc. Separating them like this allows for better packaging and safety, as the large PSU can be mounted in a different place and connected using normal connectors, rather than having to deal with very high voltages. What about auto-levelling and washers? Do I need them? Have a read here: https://www.gov.uk/guidance/mot-ins...ectors-and-electrical-equipment#section-4-1-6 If you forego them, might be worth printing out this page and taking it to your MOT to clear up and misunderstandings You can also skip the next two sections Auto_levelling The Golf system is "Static". It measure the right height at the front and rear when the lamps are switched on, then doesn't care what happens to the ride height. It may reassess at set intervals, or when the car stops, but I'm not sure. Newer dynamic systems actively tilt the bulbs to follow contours in the road. Washers Use the huge 5.5 litre washer fluid bottle, high pressure pump and pop up nozzles in front bumper. When you clean your screen with your lights on, these will fire too. Golf MK4 Xenon Types Generation 1 - Pre 2002 This is as close to a cheap eBay HID kit as you can get, except it's design and built in Germany so isn't cheap . It uses a "dumb" power supply mounted in the wheel arch on monster bracket. The PSU has 4 pins, 2 of which go to the ignitor and the other 2 are ground and +12 volts from the headlight switch. There is no diagnostics for the PSU, it either works or doesn't. The backs of the headlights have a 4-pin plug which the wire from this PSU connects too. If you look at a picture of a Gen 1 set you'll see the left and right and different. The left headlight has the silver range control module mounted to, whereas the right headlight is plain. The level sensors and K-line connect to the module on the left headlight. This module controls the motors in both headlights using the factory wiring that would normally be connected to the dial inside the car. The right headlight has no smart electronics inside. This makes Gen 1 ideal for fitting aftermarket ballasts or different bulb types as the car does not care if the bulb is running or not Generation 2- Post 2002 This is a far more modern system where each headlight has its own, combined, range control and power supply unit. The level sensors still go to the left headlight, but the two lights communicate via LIN-BUS rather than analogue signals. These headlights also have far more diagnostics features, such as being able to see the bulb power in VCDS To be contiuned
