Starting Motor - Delco 50-MT Caterpillar

The possible causes of this failure are listed below:

• The ignition switch is faulty.

• The solenoid of the starting motor is faulty.

Test Step 1. TEST THE IGNITION SWITCH

1. Use the electrical schematic to locate the "start" terminal of the ignition switch.

2. Measure the voltage at the "start" terminal while the switch is in the "run" position.

Expected Result:

The voltage should be 0 Volts.

Results:

• OK - The voltage is 0 Volts. The ignition switch is operating properly. Proceed to test step 2.

• NOT OK - The voltage is not 0 Volts. The ignition switch is not correct.

  Repair: Replace the ignition switch.

  STOP

Test Step 2. CHECK FOR ADDITIONAL CIRCUITS AT THE "S" TERMINAL

1. Locate the "S" terminal of the starter solenoid.

2. Check for additional circuits at the "S" terminal.

3. Remove any additional circuits.

Expected Result:

The starter does not operate properly.

Results:

• YES - The starter does NOT operate properly. The additional circuits are not the cause of the failure. Proceed to test step 3.

• NO - The starter operates properly. The additional circuits are causing the solenoid to latch.

  Repair: Find an alternative power source for the additional circuits.

  STOP

Test Step 3. TEST THE SOLENOID OF THE STARTING MOTOR

1. Remove the starting motor.

2. Perform the solenoid tests. See Testing and Adjusting, "Starting Motor Solenoid - Test".

Expected Result:

The solenoid is correct.

Results:

• OK - The starting motor solenoid is correct. Proceed to test step 4.

• NOT OK - The solenoid is incorrect. Replace the solenoid.

  STOP

Test Step 4. CHECK FOR SHORT TO +BATTERY

1. Disconnect the wire from the "Start" terminal of the ignition switch.

2. Disconnect the wire from the "S" terminal of the solenoid.

3. Disconnect the wire from the "S" terminal of the solenoid.

Expected Result:

The voltage should be 0 Volts.

Results:

• OK - The voltage is 0 Volts. An intermittent problem is present.

  Repair: Exit this procedure. Perform this procedure again. Look for a recurrence of the problem.

  STOP

• NOT OK - The voltage is greater than 0 Volts. The start relay has failed or a wire has a short to the + battery.

  Repair: Use the electrical schematic of the machine to test the wiring. Test the wiring between the start switch and the solenoid. If the wiring is correct replace the start relay.

  STOP