A fail-safe link for a mobile vehicle, the fail-safe link comprising: a plurality of branches connected in parallel between a power source and a load, where each of the plurality of branches contains a plurality of solid state switches (1, 2, 3, 4) having one or more varying periphery sizes connected in series between the power source and the load; and a built-in test circuit that is configured to sense an overvoltage condition across the one or more of the solid state switches having varying periphery sizes and to open or close the one or more of the solid state switches having varying periphery sizes in accordance with a measured voltage across at least one solid state switch of the plurality of solid state switches (1, 2, 3, 4), wherein the built-in test circuit comprises a Field Effect Transistor that is configured to supply a load to a solid state power controller, and a voltage sensor between a load and at least one solid state switch, wherein the voltage sensor comprises a first voltage sense line (Va) and a second voltage sense line (Vb), wherein the plurality of solid state switches (1, 2, 3, 4) comprises a plurality of Field Effect Transistors, wherein each branch of the plurality of branches contains two solid state switches (1, 2, 3, 4) which are a first solid state switch (1, 3) and a second solid state switch (2, 4), wherein load side terminals of the first solid state switches (1, 3) of each branch are connected in parallel to the first voltage sense line (Va), and wherein load side terminals of the second solid state switches (2, 4) of each branch are connected in parallel to the second voltage sense line (Vb). a plurality of branches connected in parallel between a power source and a load, where each of the plurality of branches contains a plurality of solid state switches (1, 2, 3, 4) having one or more varying periphery sizes connected in series between the power source and the load; and a built-in test circuit that is configured to sense an overvoltage condition across the one or more of the solid state switches having varying periphery sizes and to open or close the one or more of the solid state switches having varying periphery sizes in accordance with a measured voltage across at least one solid state switch of the plurality of solid state switches (1, 2, 3, 4), wherein the built-in test circuit comprises a Field Effect Transistor that is configured to supply a load to a solid state power controller, and a voltage sensor between a load and at least one solid state switch, wherein the voltage sensor comprises a first voltage sense line (Va) and a second voltage sense line (Vb), wherein the plurality of solid state switches (1, 2, 3, 4) comprises a plurality of Field Effect Transistors, wherein each branch of the plurality of branches contains two solid state switches (1, 2, 3, 4) which are a first solid state switch (1, 3) and a second solid state switch (2, 4), wherein load side terminals of the first solid state switches (1, 3) of each branch are connected in parallel to the first voltage sense line (Va), and wherein load side terminals of the second solid state switches (2, 4) of each branch are connected in parallel to the second voltage sense line (Vb).