ABYC Diesel Practice Exam

What should be done to test for voltage drop on the positive cable run during an engine crank?

1. Measure voltage at the ignition switch

2. Connect voltmeter from battery positive to starter positive

3. Check the voltage at the alternator

4. Disconnect the battery and measure lead resistance

The correct answer is: Connect voltmeter from battery positive to starter positive

To test for voltage drop on the positive cable run during an engine crank, connecting a voltmeter from the battery positive to the starter positive is the correct approach. This method directly measures the voltage drop across the length of the cable while the engine is cranking. A significant voltage drop indicates high resistance in the cable or poor connections, which can lead to insufficient voltage reaching the starter motor. By taking this measurement, you are effectively assessing the performance of the cable and its ability to handle the high current required during engine startup. A larger voltage drop suggests that there are issues that need to be addressed, such as corrosion, loose connections, or damage to the cable itself. The other options do not provide a direct measurement of the cable’s performance under load. Measuring voltage at the ignition switch, for example, would show the voltage input, but it does not reflect the voltage available at the starter during cranking. Checking the voltage at the alternator would also not indicate the condition of the starter cable, as it is upstream from the starter motor. Disconnecting the battery and measuring lead resistance does not simulate the conditions during cranking, therefore it would not yield relevant information about voltage drop.