A power supply control system for a vehicle, the system comprising: a first power control arrangement incorporating at least two inputs (3, 4) and at least two outputs (5, 6); and a second power control arrangement incorporating at least two inputs (8, 9) and at least two outputs (10, 11), each power control arrangement (2, 7) being configured to operate in an active mode or an isolated mode, wherein each power control arrangement (2, 7) comprises: a voltage input conductor (3, 8) and a voltage output conductor (5, 10); a ground input conductor (4, 9) and a ground output conductor (6, 11); a switching arrangement comprising: a first switch (28, 30) that is connected in series between the voltage input conductor (3, 8) and the voltage output conductor (5, 10); and a second switch (29, 31) that is connected in series between the ground input conductor (4, 9) and the ground output conductor (6, 11), wherein the switching arrangement is operable to configure the power control arrangement (2, 7) to operate in the active mode by closing the first and second switches so that the inputs and outputs of the power control arrangement (2, 7) are connected electrically to one another, or in the isolated mode by opening the first and second switches so that the inputs and outputs of the power control arrangement (2, 7) are electrically isolated from one another; and wherein the system further comprises: a selector arrangement which is configured to select the operating mode of the power control arrangements (2, 7) so that, at any one time, only one power control arrangement (2, 7) operates in the active mode while the other power control arrangement operates (2, 7) in the isolated mode; a DC/DC converter which incorporates inputs that are coupled to the outputs (5, 10) of the first and second power control arrangements (2, 7), wherein the DC/DC converter comprises an output which is coupled electrically to at least one device output or a plurality of device outputs which are configured to be coupled electrically to one or more other components within a vehicle. a first power control arrangement incorporating at least two inputs (3, 4) and at least two outputs (5, 6); and a second power control arrangement incorporating at least two inputs (8, 9) and at least two outputs (10, 11), each power control arrangement (2, 7) being configured to operate in an active mode or an isolated mode, wherein each power control arrangement (2, 7) comprises: a voltage input conductor (3, 8) and a voltage output conductor (5, 10); a ground input conductor (4, 9) and a ground output conductor (6, 11); a switching arrangement comprising: a first switch (28, 30) that is connected in series between the voltage input conductor (3, 8) and the voltage output conductor (5, 10); a voltage input conductor (3, 8) and a voltage output conductor (5, 10); a ground input conductor (4, 9) and a ground output conductor (6, 11); a switching arrangement comprising: a first switch (28, 30) that is connected in series between the voltage input conductor (3, 8) and the voltage output conductor (5, 10); and a second switch (29, 31) that is connected in series between the ground input conductor (4, 9) and the ground output conductor (6, 11), wherein the switching arrangement is operable to configure the power control arrangement (2, 7) to operate in the active mode by closing the first and second switches so that the inputs and outputs of the power control arrangement (2, 7) are connected electrically to one another, or in the isolated mode by opening the first and second switches so that the inputs and outputs of the power control arrangement (2, 7) are electrically isolated from one another; and wherein the system further comprises: a selector arrangement which is configured to select the operating mode of the power control arrangements (2, 7) so that, at any one time, only one power control arrangement (2, 7) operates in the active mode while the other power control arrangement operates (2, 7) in the isolated mode; a DC/DC converter which incorporates inputs that are coupled to the outputs (5, 10) of the first and second power control arrangements (2, 7), wherein the DC/DC converter comprises an output which is coupled electrically to at least one device output or a plurality of device outputs which are configured to be coupled electrically to one or more other components within a vehicle. a selector arrangement which is configured to select the operating mode of the power control arrangements (2, 7) so that, at any one time, only one power control arrangement (2, 7) operates in the active mode while the other power control arrangement operates (2, 7) in the isolated mode; a DC/DC converter which incorporates inputs that are coupled to the outputs (5, 10) of the first and second power control arrangements (2, 7), wherein the DC/DC converter comprises an output which is coupled electrically to at least one device output or a plurality of device outputs which are configured to be coupled electrically to one or more other components within a vehicle.