They are called ballasts.. its best to get either phillips or hella.. don't get those cheap korean brands.. The ML is a big car, therefore there is alot of open space to work with.. You can mount them anywhere basically.. the OEM's are mounted below the actual projectors themselves.. so when you take out the headlights you can see the ballasts underneath the assembly. I mounted mines to the metal frame that is right above the headlights.. there is like a 3 inch gap there..