Starting Motor - Delco 50-MT Caterpillar

Illustration 1	g00713118
Basic solenoid circuit

A basic four terminal starting motor solenoid circuit is shown in Illustration 1. The two windings that are found in the solenoid are the hold-in winding and the pull-in winding. The windings can be checked by using the procedures that follow.

Hold-in Winding - Test

Illustration 2	g00713128
Hold-in winding test

1. Refer to Illustration 2 in order to make the connections to the solenoid. Disconnect all other leads to the solenoid.

2. Close the switch.

   Observe the reading on the multimeter. Use the battery load tester to adjust the battery voltage until the following voltages are obtained:

   24 V System ... 20 V

   32 V System ... 28 V

3. Observe the reading on the clamp-on ammeter.

   The following amperes should be observed:

   24 V System ... 6.8 A

   32 V System ... 4.0 to 5.3 A

   Note: A high reading indicates a shorted winding. A low reading indicates excessive resistance.

4. The hold-in winding can also be checked by measuring the resistance.

   Disconnect the batteries. Select the "200 ohm" range on the multimeter. Connect one of the leads of the multimeter to the "S" terminal and connect the other lead to the "G" terminal.

   The following Ohms should be observed:

   24 V System ... 2.9 Ohms minimum

   32 V System ... 5.3 to 7.0 Ohms

5. Replace the solenoid if any of the above readings are incorrect.

Pull-in Winding - Test

Illustration 3	g00713129
Pull-in winding test

1. Refer to Illustration 3 in order to make the connections to the solenoid. Disconnect all other leads to the solenoid.

2. Close the switch.

   Observe the reading on the multimeter. Use the battery load tester to adjust the battery voltage until the following voltages are obtained:

   24 V System ... 20 V

   32 V System ... 28 V

3. Observe the reading on the clamp-on ammeter.

   The following amperes should be observed:

   24 V System ... 9.0 to 11.5 A

   32 V System ... 7.0 to 8.3 A

   Note: A high reading indicates a shorted winding. A low reading indicates excessive resistance. To avoid excessive heat, do not leave the switch closed for more than 10 seconds at a time. The current will decrease as the heat increases.

4. The pull-in winding can also be checked by measuring the resistance.

   Disconnect the batteries. Select the "200 ohm" range on the multimeter. Connect one of the leads of the multimeter to the "S" terminal and connect the other lead to the "Mtr" terminal.

   The following Ohms should be observed:

   24 V System ... 0.43 to 0.56 Ohms

   32 V System ... 1.20 to 1.43 Ohms

5. Replace the solenoid if any of the above readings are incorrect.