That's odd adding the relay doesn't solve your guys' issue considering all the factory wiring system and controls are merely actuating that relay now which doesn't take any power at all to do and the HIDS are on it's own power and ground source from the relay.
I would instead, supply a separate new ground wire for the relay instead of using the factory ground wire off the fog harness. Leave the factory fog harness ground alone and just use the positive side to trigger the relay. Also wire in a diode so there is no chance of back feeding. This way will ensure that only the positive lead of the factory fog harness is being used to power the relay and the diode should eliminate any odd back feeding messing with your lights.
EDIT: I just realized that some of the relay harnesses you can buy might have different relay circuitry types as there are a few variations of how you can wire a basic relay. I always make my own relay harnesses so I know what pin is going to what.
02 Carbon Black M3 6MT
456whp/312wtq @ 8psi, No #'s yet at 9.5psi
4.10 / Headers / ESS VT2-550+
Last edited by Tchleung; 01-05-2013 at 08:00 PM.