Warning Horn Wire Diagram-Tiller Handle Models; Ignition Components; Flywheel/Timing Belt Cover; Flywheel Assembly - Mercury 25 EFI Service Manual

Ignition
Warning Horn Wire Diagram—Tiller Handle Models
18 1
1
11
34 17
a - ECM engine harness connector
b - Warning horn

Ignition Components

Flywheel/Timing Belt Cover

The purpose of the flywheel cover is to provide basic protection against accidental contact with the flywheel, starter motor
pinion gear and camshaft drive belt while the engine is running.
Removal of the flywheel cover provides access to the flywheel, camshaft drive belt tensioner, camshaft drive belt, starter motor
pinion gear, and the crankshaft position sensors.

Flywheel Assembly

The flywheel is weighted and balanced to improve engine running characteristics. The flywheel is secured to the crankshaft
with a washer and nut. The flywheel has a ring gear that is used with the starter motor to start the engine electrically. Below the
ring gear, the flywheel is cast with a timing key. As the timing key passes the first crankshaft position sensor (CPS), an
electrical pulse is generated within the CPS and is sent to the Electronic Control Module (ECM). The ECM then calculates the
position of the crankshaft based on the electrical pulse generated when the timing key passes the second CPS. The ECM will
use this information to regulate ignition and fuel injector timing. The flywheel also has magnets on the inside circumference to
generate AC voltage needed for the ECM to operate. These same magnets are also used to generate voltage to charge a
battery.

Stator

The stator is located under the flywheel. The stator is composed of several layers of steel plates called a bobbin laminate. The
bobbin laminate is wound with a fine wire in order to generate a high voltage that is required for the ECM, ignition coils, and
high pressure fuel pump to function. There are three separate windings on the stator that supply voltage for a specific
component within the fuel system, ignition system, and battery charging system. As the flywheel rotates, magnets secured to
the inside of the flywheel pass close to the stator bobbins, generating a strong alternating current. The AC current is sent to the
ECM where it is rectified to direct current (DC) voltage to energize the ECM, high pressure fuel pump, IAC, fuel injectors, and
the warning system. There is also a heavy gauge wire wound on the bobbins to generate voltage required to maintain the
battery. This voltage is rectified external of the ECM.
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© 2016 Mercury Marine
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22603
90-8M0105568 eng MARCH 2016