Sounds like a bad ground or a ground 'loop'. Just my .02. Good luck. Fwiw, I have my hid's pos. and neg. connected directly to the battery.
2001 Extended cab Edge, 4x4, 4.0, 4.10 gears, 3" PA body lift, Heartthrob dual exhaust, Roush Thunderbolt signal mirrors, 8000k hid head/foglights, Mountaineer leather buckets, Xplorer shorty console, Alpine 9856 receiver, 10" type r sub in ported box, air box mod, throttle cable mod, Rancho R5000 shox, Scangauge II, plus many other things...