my glow plug light only stays on for 3 seconds ?

most likely to be the glow plugs they wear out one at a time so when theres less of them light goes of sooner. dewire them and test one at once with a 12v bulb off live on battery to terminal for wire .do not turn on the ing as it will burn out the relay box if the wire from heater plugs earths.if they are ok the bulb will light.if you need to test relay run wire from one of terms through bulb to earth it will light bulb and carry on for a while after light goes off when you turn ing on

bob
March 2012