Those HID lights look great!
To those of you installing H4 bulbs, yes, you will certainly want to switch over to relays for your headlight's power. Dragging that much current through the harness and the wee wires puts a lot of stress on the switch and wiring.
I did the relay switch last summer, and my headlights were a LOT brighter (I have H4 bulbs), it was amazing.
Now for those HIDs, did you have problems fitting them in the shallow buckets of the '66?
Relay trick: Brighter Headlights
It only took about 2 hours, and was very easy. If you don't like the relays on the fender apron, you can hide then in the fender or under the battery as a few on this forum have.
1966 289-2V C-4 Convertible. 2nd owner, resurrected rustbucket. Factory console and power top, conversion to P/B with dual res MC.
1990 GT 25th Anniversary 5.0 AOD Convertible. SOLD