Frostytel

Think my ballast unit may have packed up, have fitted new bulb no change, swapped igniter modules from one side to the other still no change however the module from the side that wasn't working works when fitted to the bulb on the good side ...... When first investigating problem I opened plastic cover to gain access to igniter and bulb and found igniter had some how fallen off back of bulb, would this have cooked ballast ? ... Is it possible to change / try a new replacement ballast without removing bumper or could it be a fuse ( no fuse allocation chart in car ) not sure which one to look at ! , it's a w164 2006 ml320