neverarelayagain

hi everyone,i have a problem that no garage seems to be able to fix,the horn,heater and reverse lights have stooped working(all stopped at the same time).all fuses have been checked and are ok but there is a clicking sound in the fuse box under the bonnet,similar to an indicator being used.would this be a wiring fault or relay fault,did get this error on last mot,,Offside Rear Direction indicator adversely affected by the operation of another lamp (1.4.A.2h).dont know if that would cause any other wiring faults.thanks all who take the time to look or comment.