An in-vehicle system is provided with a first in-vehicle unit having a first electric signal transfer part, a first substrate wiring, and a first connector; a second in-vehicle unit having a second electric signal transfer part, a second substrate wiring, a third substrate wiring, a second connector, and a third connector; a third in-vehicle unit having a third electric signal transfer part, a fourth substrate wiring, a fifth substrate wiring, and a fourth connector; a first insulated sheathed cable connecting the first connector and the second connector; and a second insulated sheathed cable connecting the third connector and the fourth connector. When the first insulated sheathed cable is connected, the first substrate wiring and the third substrate wiring become conductive. When the second insulated sheathed cable is connected, the second substrate wiring and the fifth substrate wiring become conductive, and the third substrate wiring and the fourth substrate become conductive.