2004 GMC ENVOY HEADLIGHTS WOULD PERIODICALLY DIMM AND GO OFF DURING BREAKING. WITHOUT WARNING HEADLIGHTS FAILED WITH NO INDICATION. REPAIR AT GMC DEALER COST $130 FOR A "HDM RELAY". VERY DANGEROUS FAILURE AS NO FUSES FAILED, NO LAMPS FAILED, BUT A HIDDEN COMPONENT FAILED WHICH CAUSED ME TO GO OFF A HIGHWAY AT HIGH SPEED AT NIGHT. *TR