Cummins ISX11.9 CM2250 – Service Manual 013-030   Key Switch

WARNING  Be sure the key switch is in the OFF position to reduce the possibility of electrical shock and personal injury.

Remove the wire connecting the keyswitch to the magnetic switch (marked S or Start) from the keyswitch terminal.

Connect the positive (+) lead of digital multimeter, Part Number 3377163, or equivalent, to the keyswitch terminal and the negative (-) lead to a chassis or engine ground location.

Set the multimeter to indicate DC volts with the keyswitch in the OFF position. There must be no voltage at the keyswitch terminal.

If the meter indicates voltage, the keyswitch is malfunctioning and must be replaced.

• Turn the keyswitch to the START position.

The multimeter must indicate system voltage.

If there is no voltage:

• Turn the key switch to the OFF position.
• Check for supply voltage to the keyswitch by connecting the multimeter positive (+) lead to the key switch terminal having a wire connecting the keyswitch to the starter motor solenoid “B” terminal.

• Turn the keyswitch to the START position.

If the meter indicates system voltage at the key switch input terminal, the key switch is defective and must be replaced. Refer to the OEM service manual for replacement.

If the meter indicates no voltage, the switch is not the cause of the complaint.

Check the wiring from the keyswitch to the starter motor solenoid “B”
terminal, and from the starter motor solenoid to the battery, for broken or damaged wires.