You should be pulling fuse #17 and 18, from the engine bay fuse box when on the dyno (or any other time you want to totally disengage ABS/ESP). When these fuses are pulled, you will get the ABS/ESP lights on the dash, the systems will not engage, but nothing elses should be impacted. I drive my car like this very often. Not sure what connector you pulled to have lost a fastener nut.