K.. check all the 6-8 prong MAIN connector.(behind the headlight-main harness) I´ve had that happen once, bend the headlight connectors to the outside a little. Vibes sometimes cause bad connectons. Try DI-ELECTRIC GELL on the contacts(metal blades on back of light)If ya don´t have any, vasoline works great.. especially on batt. terminals.. I´m sure its a bad contact/ground or round snap together wire connector(s). I´ve had bizzar things happen like both front running lights (signals) go out because of that. They blinked to turn, just didn´t light up same as rear for some odd reason. LOL (running lights)Just use a LITTLE of the gel or vasoline. Too much will cause ohms travel and slowly drain/short your battery out..k? Good luck man!! :D