My HID bulb(s) won’t turn on at all or won’t stay on anymore. How do I figure out what is wrong?
Always check fuses first when a light is out. This is easy to check and easy to fix if found to be the issue. If the fuses are all ok, you should then double-check the wiring to make sure it is all connected.
If you’ve ruled out fuse and wiring issues, this generally only leaves the components (ballasts and bulbs). If only one side (driver or passenger) is out, just swap parts from side to side. Start by swapping bulbs first, because they are usually easier to get to (at least in OEM setups). If the problem follows the bulb, then it is obviously a problem with the bulb. If the problem stays with the headlamp, it is the ballast.
Why are my HID headlamps flickering and/or turning off shortly after being turned on?
This could be a loose connection in the wiring or bad components (bulb or ballast), but the most common problem I've seen with flickering HID lamps (when they are added to a vehicle that did not come with them from the factory) is low voltage at the input to the ballast during startup.
OK, so why is the voltage too low at the ballast during startup?
This could be a low battery (or alternator going bad resulting in a low battery), but the most common problem is the “natural” voltage drop in the stock vehicle wiring (for power and ground to the ballast) due to resistance that is higher than the HID system was designed for.
Why is the resistance in my vehicle wiring too high for HID?
Most vehicles are designed to only use the minimum gauge of wiring necessary for the factory equipment planned for that vehicle. There is no reason for “overkill” since it costs more money and isn’t necessary from an OEM perspective.
Electrically, it works like this: HID ballasts have a very high inrush current (relative to their steady state or in comparison to halogen) that is required to "fire" or ignite the arc in the lightsource. The wires carrying this current and providing power to the ballast (regardless of size) and connector terminals, etc. have some fixed resistance (R).
During the inrush period of an HID system, the current (I) spikes high (typically 20-30Amps for OEM ballasts). So, based on V=IR (where V = the voltage drop over the given resistance, which is wires in this case), you can see that this “much higher than halogen” inrush current results in a much larger voltage drop (V) than would be seen with the stock halogen source...which often results in a voltage at the input to the ballast that is below the functional design intent while trying to start. Once the HID system has “fired” and reached steady state (i.e. warmed up), the current lowers to a level (typically down to only 3-4Amps for OEM ballasts) that is actually lower than that of halogen.
So math aside, the issue is typically resistance...which is why it is recommend to use relay harnesses when adding HID to a vehicle that had halogen before. In doing so, it allows you to use a larger gauge of wire (i.e. smaller resistance) and connect directly to the battery (which is typically a lower resistance path). This combination results in less of a voltage drop in the wiring, and a higher voltage at the input to the ballast.
How do I buy or build, and install a relay harness?
To buy: I recommend contacting a2b4guy here on the vortex. He builds and sells these for many vehicle types and is a good guy from my experience.
To build: Follow one of the diagrams below. You can purchase the components at a Radio Shack type of store (at the store or online), or at just about any auto parts store.
Harness type 1: This is the easiest type of harness to make and only uses one relay. Under normal conditions, this is fine to do. However, the risk of using only one relay (and one fuse) for both sides is that if either goes bad, you lose both headlamps until you fix it.
Harness type 2: This takes more components than the harness above (2 relays and 2 fuses), but it is more reliable in theory. Here, if one fuse or one relay goes bad, you only lose the respective headlight, and you still get light from the other one to "limp" home.
A typical automotive relay looks like this:
and has a pinout like this:
Regardless of which harness "type" you use, you should make sure that the relay is mounted with the "tab" up so that the wiring comes out the bottom and water can't run into it. Really, all wiring should be given a "drip-loop" near the input to connectors to ensure that water can't run *down* the wiring into the device.
Why is it the passenger side HID lamp that typically has issues on the mkIV VW platforms?
In short, the passenger side is farther away from the battery. The fixed resistance (R) mentioned above is larger for the passenger side due to this longer run of wiring between the headlamp/ballast and its power source. This higher resistance results in a higher voltage drop in the wiring, and a lower voltage at the input to the ballast.
I’ve installed a relay harness, but I’m still having problems…what could be wrong?
Again, it could be loose connections or a low battery. It is also possible that the harness you installed didn’t have a low enough resistance (which is the case in some of the aftermarket relay harnesses that come in the “kit”).
A good rule of thumb is to ensure that the total resistance of the circuit between the battery and the ballast (including both power and ground leads) is less than 120m ohms (0.120 ohms). If you have a digital multimeter, it most likely has the ability to measure resistance. Use this to measure the resistance between the ballast input connector and the battery (with the ballast disconnected). You'll probably want to measure the power lead and the ground lead separately, and you can just add the measurements to get the total resistance. The same addition rule applies for measuring each section of the wiring separately (i.e. from ballast to relay, and from relay to battery), which is necessary to do if you don't have the relay energized to "complete" the connection.
If you only have a voltmeter (i.e. not a multi-meter), you can measure the voltage at the input to the ballast, but it has to be measured during the inrush period of the ballast (with the ballast connected) to see what the voltage falls to. You'll probably need two people to do this...one to take the measurement and one to turn the lights on. The voltage will change quickly and you'll just have to watch for the lowest number. This is a crude method (compared to using an oscilloscope), but will generally get the job done. It should remain above 8V during inrush for most ballasts (above 9V for some) for it to work correctly. If the ballast is toast and won't even try to start, then the voltage measured will simply be the battery voltage (not changing rapidly) and won't tell you much.
When doing this voltage measurement (or any "probing" of the HID system), make sure that you only probe the INPUT to the ballast. This is DC voltage and is relatively low. DO NOT try to measure the OUTPUT of the ballast, as this is a HIGH VOLTAGE that can be very DANGEROUS).
If it is not a resistance problem, it is possible that the damage has already been done, and that it is too late to “fix.” Still, the relay harness (with larger wiring) is a good idea to protect your HID system going forward (when you get a new ballast or bulb to replace whichever is bad).
Will HID melt my headlamp?
HID bulbs actually put out LESS heat than halogen. It is a more efficient source, creating more light with less power consumption.
work in progress...more to come as time allows