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Outboard motor electronics are sometimes troublesome, particularly since major systems like the power pack may control everything from instrumentation to the timing and synchronization of the motor. You can test the Mercury power pack in either one of two ways; one method requires you to use a multimeter, to test the power pack directly. The other method requires you to do a bit more work, but may give you a more definitive answer.
Items you will need
Functional power pack
Testing With a Multimeter
Note the routing and connection points, then disconnect the primary wire or wires from the ignition coil. Disconnect and test one coil at a time when testing multiple ignition coils on the same motor to help prevent confusion when reconnecting the wiring.
Select the resistance scale on the multimeter. Place the positive probe of multimeter on the green and white striped terminal wire pin and the negative probe of the multimeter on the terminal pin for the red and yellow wire. Primary resistance should be less than 1 ohm, about 0.38 ohms and 0.78 ohms. Check the ignition coil secondary resistance between the spark plug lead tower and the ground terminal pin for the black wire; the meter should show between 8100 ohms and 8900 ohms.
Repeat the process to ensure that you only probed the proper wires and connectors if tests are out of specification. Make sure the ground was good -- not painted or insulated when checking with a ground on the motor.
Replace the coil if readings are out of specification after re-testing, and if no other causes can be discovered. Reconnect the wiring when the testing is complete.
Testing With a New Power Pack
Contact your dealer and arrange to borrow a power pack that is known to be functional.
Remove one wire from the suspect power pack. Plug it into the appropriate connection on the functional power pack. Continue to remove and reconnect wires until all of the wires are removed from the suspect power pack and connected to the functional power pack. Ground the functional power pack to the motor.
Start the motor. If the problem is resolved, the problem lies with the power pack. If the problem persists, the problem lies elsewhere.
- Mariner/Mercury Outboards Repair Manual, 2.5-250 HP, 1990-2000; Seloc Marine
Will Charpentier is a writer who specializes in boating and maritime subjects. A retired ship captain, Charpentier holds a doctorate in applied ocean science and engineering. He is also a certified marine technician and the author of a popular text on writing local history.