Mercury 90 Service Manual

90-830234R3 DECEMBER 1997 ELECTRICAL - 2A-19
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.
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.

Mercury 90 Specifications

General

Brand	Mercury
Model	90
Category	Outboard Motor
Language	English