Theory Of Operation - Mercury 75 Service Manual

3 CYLINDER MODELS –
Disconnect the BLUE adapter lead from the
switch box.
Connect the DVA meter between the BLUE
adapter lead and ground.
Crank the engine (manual or electric).
If the DVA is normal (190 to 260 volts), the switch
box is defective.
If the DVA reading is still low, either the stator or
the adapter is defective.
Disconnect the GREEN/WHITE and WHITE/
GREEN stator leads from the adapter.
Measure the resistance between the GREEN/
WHITE and WHITE/GREEN stator leads.
If the resistance is normal (660 to 710 ohms), the
adapter is defective.
If the resistance is incorrect, the stator is defec-
tive.
90-830234R3 DECEMBER 1997
4 CYLINDER MODELS –
Disconnect the BLUE adapter lead from the
switch box.
Connect the DVA meter between the BLUE
adapter lead and ground.
Crank the engine (manual or electric).
If the DVA reading is normal, reconnect the BLUE
adapter lead to the switch box.
Disconnect the BLUE/WHITE adapter lead from
the switch box.
Connect the DVA meter between the BLUE/
WHITE adapter lead and ground.
Crank the engine (manual or electric).
If the DVA reading is normal (190 to 260 volts),
the switch box is defective.
If either of the DVA readings is still low, either the
stator or the adaptor is defective.
Disconnect the GREEN/WHITE and WHITE/
GREEN stator leads from the adapter.
Measure the resistance between the GREEN/
WHITE and WHITE/GREEN stator leads.
If the resistance is normal (660 to 710 ohms), the
adapter is defective.
If the resistance is incorrect, the stator is defec-
tive.

Theory of Operation

This outboard ignition system is alternator driven
(distributor-less) capacitor discharge system. Major
components of the ignition system are the flywheel,
stator, trigger, capacitor discharge modules (CDM's)
and spark plugs. Each capacitor discharge module
functions as a combination switchbox and secondary
ignition coil.
NOTE: The following schematics are for 3 cylinder
models. The circuitry would be very similar for the 4
cylinder models with the addition of a another CDM.
3 cylinder models have 3 trigger coils and 4 cylinder
models have 4 trigger coils.
ELECTRICAL - 2A-19