This is how I fixed mine (I have the Bi-Xenon). Hope this helps!
Here is the right side factory pigtail with the capacitor plugged directly into the empty pigtail. Negative to positive and vice versa.
Here is the left side with the HID harness plugged into the factory pigtail. I had to split the casing of the HID wires to attach the capacitor to them. Again, negative to positive and vice versa.
These are 1000uf 35v electrolytic capacitors from Radio Shack. They cost a whopping $1.62 each and stopping my flickering issues. These capacitors have been in for about 7 months now. Don't mind the mess, I had to peel off the electrical tape for the pics and we all know how messy that can be with some good ol Super 88.