Does it do it on HID start up, or all the time they are running? Have you tried hanging the ballast out of the bike as far as you can get it to see if it makes a difference? If you unplug the ballast do the symptoms go away? Have you tried re-routing the cabling?

Shielding the cables with foil isn�t a bad idea, but unless the screen is earthed, it isn�t going to make a massive difference to any interference from electromagnetic fields.

Quite often this sort of problem is more likely caused by conducted interference (not electromagnetic fields) where high voltage/high frequency signals are coupling directly to other parts of the bike�s electrical system (via the chassis/frame) known as capacitive coupling.

The battery negative is connected to the frame, but I�d guess nowhere near where your ballast is mounted? I assume it�s mounted up front somewhere? Therefore the return currents from the interference source (the ballast) are likely to follow a very long path back to the negative battery terminal. Any other electronics using the frame as a ground reference or earth (which is just about everything � ECU, dash etc.) will be affected by this conducted interference. In fact it is highly likely that other electronic systems are being effected too, but you�re only noticing the speedo doing funny things because it�s in your face.

There are a couple of things you could do to minimise the unwanted effects of conducted interference:

One way round this is to run all the HID wiring direct to the battery terminals (feed via diode protected relays to do the switching), particularly the earth/ground cable. Avoid just plugging it in to the existing harness for the headlamp. This will greatly reduce the potential for conducted interference.

You could also try inductors or chokes (ferrite cores) on the cables which may reduce interference further. You can buy chokes from electronics shops cheaply, or take them off old computer power cables. Capacitor(s) or suppressors fitted across the ballast will help a lot too, especially if you connect them as close to the ballast as possible. Maybe try a 10,000uF capacitor for starters? The capacitor must be fitted directly across the power and ground terminals as close as you can get to the ballast and any choke(s) fitted close by on the supply cable. Fitting capacitors is the same technique used on cars to suppress alternator and ignition systems to protect electronics and prevent radio interference.

Otherwise try/substitute a different ballast from another source.

Some HIDs seem to cause these sorts of problems and others don�t? One person fits a kit and its� fine, another has trouble. It�s probably down to the varying quality of the electronics supplied in the kits. OEM HIDs/ballasts for example are screened, suppressed and their operating frequencies carefully thought about, which is why they are expensive and I guess why the Chinese kits are cheap?

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