My images of fox info are not good quality but hope this helps:
The disc brake switch works off compression with an oring sandwiched in between the metal discs on the caliper arm stud, the plastic flanged washers also need to be on there and in good shape so the discs do not touch anything else that can ground them and the oring needs to keep them separated enough to not connect when the brake is not applied but be flexible enough so that the discs can touch each other when you pull the lever.