See the tech article on this in the Pelican Site.
http://www.pelicanparts.com/techarticles/mult_h4_headlamps/mult_h4_headlamps.htm
This is one of the first upgrades I did to my car. I think the bulbs I have are 55/100 or 55/80? Man are they nice for a drive in the mountains at night.
I did not install the optional relay and while everything works fine, it is probably a good idea. I talked with one of the guys on the phone at Pelican and he said that he had them in his car without the extra relay and no problem...
Still I may put the relay in later anyway as it seems like too much power to be pulling through the normal circuit. I have had mine for a little less than a year with no problem from cooked wires yet.
I lost one bulb due to one of the headlamps rattling around I think. You can pick up spares at an off road car or motorcycle place. The FLAPS don't usually carry them since they are not DOT legal for street use... too bright!
- Dave