The result of these switches and relays is to permit a 5 amp dash-mounted switch to turn on a 500 to 1000 amp motor used to crank an engine. If the starting motor cranks real slow or does not crank at all, do the following procedure: Battery voltage (power) available during cranking varies according to the temperature of the batteries. The following chart is a guide as to what to expect from a normal system. 1. Measure battery voltage at the battery posts with the multimeter while cranking or attempting to crank the engine. Make sure to measure the battery posts. Do not measure the cable post clamps. 2. Is battery voltage equal to or greater than shown in Figure 1?
I If the battery voltage is correct, go to Step 3. I If the battery voltage is too low, Charge or replace the battery. NOTE: A low battery can be caused by battery condition or a shorted starting motor. Figure 1 3. Measure current draw on the (+) battery cable between the battery and the starting motor solenoid with the clamp-on ammeter. The maximum current draw allowed is 350 Amp. At temperatures below 27°C (80°F), the voltage will be less and the current draw will be higer. If current draw is too much, the starting motor has a problem and must be removed for repair or replacement.
The next chart shows maximum acceptable voltage loss in the high current battery circuit feeding the starting motor. These values are maximums for machines of approximately 2000 SMH and up. Newer machines would be less than those shown. NOTE: If voltage at the battery post is within approximately 2 volts of the lowest value in the applicable temperature range of Figure1 and if the large starting motor cables get hot, then the starting motor has a problem and the Ammeter test is not needed. Figure 2 4. Measure starting motor voltage from test point (4) to (5) with the multimeter while cranking or attempting to crank the engine.
Voltages greater than those shown are most often caused by loose and/or corroded connections or defective switch contacts. 5. Is voltage equal to or greater than shown in Figure 1? I If the starting motor voltage is correct, the battery and starting motor cables down to the motor are within specifications. Go to Step 8. I If the starting motor voltage is low, the voltage drop between the battery and the starting motor is too great. Go to Step 6. Diagnosis Procedure NOTICE Do not operate the starting motor for more than 30 seconds at a time. After 30 seconds, the cranking must be stopped for two minutes to allow the starting motor to cool.
This will prevent damage to the starting motor due to excessive heat buildup. 6. Measure the voltage drops in the cranking circuits with the multimeter. Compare the results with maximum voltage drops allowed in Figure 2.
G424 Service Manual Starting System 34 TYPICAL SYSTEM VOLTAGE DURING CRANKING AT VARIOUS AMBIENT TEMPERATURES Temperature 12V System -23 to -7 C (-10 to 20 F) 6 to 8 Volts -7 to 10 C (20 to 50 F) 7 to 9 Volts 10 to 27 C (50 to 80 F) 8 to 10 Volts MAXIMUM ACCEPTABLE SYSTEM VOLTAGE DROPS DURING CRANKING Circuit 12V System Battery(-) post to starting motor (-) terminal 0.7 Volts Battery (+) post to solenoid (+) terminal 0.5 Volts Solenoid Bat terminal to solenoid Mtr terminal 0.4 Volts TOOLS NEEDED Digital Multimeter or Equivalent 1 DC Clamp-On Ammeter or Equivalent 1