unit u2014 starter control unit scu the control unit scu has various inputs and outputs including kl 87 kwr canh canl emergency off kl 31 gnd vehicle gnd kl 30 p kl 50 r kl 50 s kl 45 kl 50 t the control unit is grounded by means of a screwed connection to the motor kl 31 is the battery ground kl 30 therefore denotes a supply of the battery with a voltage of 12v kl 50 denotes the direct energization of the holding winding hw and of the engagement winding enw from the motronic unit kl 30 p denotes the connection to the 12v battery supply in the control unit scu kl 50 r denotes the connection to the 12v supply to the holding winding hw the engagement winding enw and the switching winding stw kl 50 s denotes the connection to the ground of the switching winding stw kl 45 denotes the connection to the 12v battery supply from the control unit scu that is to say starter energization when the switching elements s 1 to s 3 switch the latter being switched together or individually kl 50 t denotes the connection to the ground at the holding winding hw and the engagement winding enw s 0 denotes a main switch of the control unit scu by this means the.