Hello , hope i'm not repeating posts if so please tell me , got problem with my Focus ; when cold in the morning starts no problem , no smoke no rattles everything's fine , drive few miles or even longer leave the car standing for half an hour or so and can't start , glow plugs are new , service just done filters, oil etc ,checked that there is no voltage on the plugs , gave him 12 v from battery when doesn't want to start and starts straight away ,noticed that glow plug light comes off after a second or second and half when doesn't wanna start , when normally stays there for few seconds , looked up under bonnet and looks like there are 3 relays , what You suggest ? changed all 3 of them ? help please... many thanks