Outboard Ignition Troubleshooting – Page 36 – Voltage Drop Measurement
This page explains voltage drop testing for battery cables, ignition feeds, and charging system grounds. In many cases, a voltage drop test is more useful than a simple ohmmeter reading when tracking down bad cables, poor connections, or undersized conductors.
Voltage Drop Measurement
Use a good digital auto-ranging voltmeter capable of reading tenths of a volt. An auto-ranging meter helps improve accuracy and reduces the chance of damaging the meter by selecting the wrong range.
Before testing, remove the spark plug wires from the spark plugs and connect them to a spark gap tester. Remove the emergency stop clip as well. This helps prevent the engine from starting and reduces the chance of shock from the ignition system. Also remove and clean all battery cables and connection points before testing.
Testing the Positive Battery Cable to the Engine
- Select the DC volts position on the meter.
- Connect the red positive lead of the meter to the positive battery post.
- Connect the black negative lead of the meter to the starter solenoid terminal where the positive battery cable is connected.
- Using a remote start switch, activate the starter solenoid to spin the engine and observe the reading on the meter. A reading above 0.6V indicates a bad cable or bad connection.
(A) If the meter reads above 0.6V, move the black lead of the meter to the positive battery cable terminal on the starter solenoid and retest. If the reading drops below 0.6V, the cable connection is bad.
(B) If the meter still reads above 0.6V, move the black lead of the meter to the positive battery cable terminal on the battery and retest. If the reading drops below 0.6V, the cable is bad or undersized.
(B) If the meter still reads above 0.6V, move the black lead of the meter to the positive battery cable terminal on the battery and retest. If the reading drops below 0.6V, the cable is bad or undersized.
Service Note: A bad power connection to the ignition or battery charging system can be found by connecting the black lead of the meter to the power connection of the ignition or charging system and working your way back toward the battery positive post. At no time should you see a reading above 1V.
Testing the Negative Battery Cable to the Engine
- Select the DC volts position on the meter.
- Connect the black negative lead of the meter to the negative battery post.
- Connect the red positive lead of the meter to the engine block where the negative battery cable is connected.
- Using a remote start switch, activate the starter solenoid to spin the engine and observe the reading on the meter. A reading above 0.6V indicates a bad cable or bad connection.
(A) If the meter reads above 0.6V, move the red lead of the meter to the negative battery cable terminal on the engine block and retest. If the reading drops below 0.6V, the cable connection is bad.
(B) If the meter still reads above 0.6V, move the red lead of the meter to the negative battery cable terminal on the battery and retest. If the reading drops below 0.6V, the cable is bad or undersized.
(B) If the meter still reads above 0.6V, move the red lead of the meter to the negative battery cable terminal on the battery and retest. If the reading drops below 0.6V, the cable is bad or undersized.
A bad ground connection to the ignition or battery charging system can be found by connecting the red lead of the meter to the ground connection of the ignition or charging system and working your way back toward the battery negative post. At no time should you see a reading above 1V.