are you using a same common wireing harness on both? double check and be sure there are not any stuck or broken pins, also check and see if the harness is in tact and none of the pins are touching. lastly if those are fine plug it in then touch one of the bulbs with your finger, if the bulb shows any signs of light at that point then you have a bad ground.

unfortunately icecap is out of business for the time being but they may be back up and running soon. evil had stated a while back that workhorse 7's are the only workhorse that overdrives the bulbs so you could possibly try to use that as a replacement.