Starting System
Page 4A-10
90-864260200 AUGUST 2009
Starting System Tests
Voltage Drop Test
Low power supply voltage and water contamination are the primary causes of most starter motor failures. Low power supply
voltage causes excessive heat to build up in the starter motor. It can also cause starter motor solenoid contact problems.
IMPORTANT: Perform these tests with a digital voltmeter before removing the starter from the engine.
1. Set the digital voltmeter to 0 before testing.
2. Ensure that the battery is fully charged.
3. Remove the coil wire from the distributor cap and ground it to prevent the engine from starting.
4. Connect the voltmeter positive (+) lead directly to the large, threaded terminal.
5. Connect the voltmeter negative (‑) lead directly to an unpainted metal surface on the starter housing.
6. Crank the engine over with the key switch for 10‑15 seconds while observing the voltmeter.
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A voltmeter reading of 9.5 volts or more indicates that the battery is supplying sufficient voltage to the starter to operate
properly. If the starter does not function properly, the starter or the engine are malfunctioning. Remove the spark plugs
and try turning the engine over by hand to rule out an engine problem.
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A voltmeter reading below 9.5 volts indicates a voltage loss between the starter motor and the battery. Check all
components between the starter motor and the battery for damage, wear, and proper application.
Low Voltage Test
1. Test the battery positive (+) cable first. Connect the voltmeter positive (+) lead directly to the positive (+) post of the battery.
Do not use the battery cable terminal. Connect the voltmeter negative (‑) lead directly to the large, threaded starter motor
positive (+) terminal to which the battery positive (+) cable is connected.
NOTE: Remove one voltmeter lead before starter motor is turned off or voltmeter damage may occur. The starter may produce
a voltage spike that can damage a voltmeter.
2. Crank the engine over while observing the voltmeter. The maximum allowed drop is 0.25 volts.
3. To find the point where the resistance is highest, leave the voltmeter positive (+) lead on the battery post and move the
voltmeter negative (‑) lead to the battery positive (+) cable ring terminal, which is on the threaded starter terminal.
4. Move voltmeter negative (‑) lead to the battery cable itself, which is inside the crimped battery cable ring terminal.
5. Continue to test each battery cable connection back to the battery positive (+) post. If a battery switch is used, check between
the battery cable ring terminal and the switch's terminal.
6. Check for voltage drop on the battery negative (‑) cable. Connect voltmeter negative (‑) lead directly to the battery negative
(‑) post, not the battery cable ring terminal. Connect voltmeter positive (+) lead to an unpainted surface of the starter housing.
NOTE: Remove one voltmeter lead before starter motor is turned off or voltmeter damage may occur. The starter may produce
a voltage spike that can damage a voltmeter.
7. Crank the engine over while observing the voltmeter.
IMPORTANT: The maximum allowed drop is 0.25 volts.
8. To find the point where the resistance is highest, leave voltmeter negative (‑) lead on battery negative (‑) post and move
voltmeter positive (+) lead to the ground stud where the battery negative (‑) cable is connected.
9. Move the voltmeter negative (‑) lead to the battery negative (‑) cable ring terminal that is on the ground stud.
10. Move the voltmeter positive (+) lead to the battery cable itself, which is inside the crimped battery cable ring terminal.
11. Test each battery cable connection in this manner back to the battery post.
12. After testing to ensure that the starter motor is getting at least 9.5 volts, test the starter motor solenoid for at least 9.5 volts
from the slave solenoid during cranking. Low voltage at the starter solenoid can cause intermittent operation of the solenoid
contacts and shorten the life of the solenoid.
13. Connect the voltmeter positive (+) lead to the terminal on the starter solenoid with the YEL/RED wire from the slave solenoid
connected to it.
14. Connect the voltmeter negative (‑) lead to unpainted surface of the starter housing.
15. Crank the engine over and observe the voltmeter. If the starter solenoid is not getting 9.5 volts, the YEL/RED wire or the slave
solenoid could be the cause of the low voltage.
Water and Corrosion Inspection
1. Remove the 2 short screws from the starter motor end cap and inspect the threads.
2. If they are clean and gold in color, the starter motor has not had water inside of it.
3. If they are dirty and discolored the starter motor may have water contamination and should be replaced.
IMPORTANT: Starter damage caused by water contamination is not covered by the Mercury MerCruiser warranty.
