Outboard Ignition Troubleshooting – Page 20 – Mercury Alternator Driven Ignition Systems
This page covers Mercury alternator driven ignition systems for two cylinder engines, including 1979–1997 models using the 332-7452 switch box and 1994–1998 models using the 18495 switch box.
Mercury Alternator Driven Ignition Systems
Two Cylinder Engines
Two Cylinder Engines
Note: These engines sometimes develop a condition where only one cylinder fires. One cause can be loose flywheel magnets shifting until they touch. If only one cylinder is firing, remove the flywheel and verify the magnets are tightly bonded.
1979–1997 Models
(With 332-7452 Switch Box)
(With 332-7452 Switch Box)
No Fire At All
- Disconnect the black/yellow kill wire and retest. If the ignition system now fires, the kill circuit has a problem.
- Check the stator resistance and DVA output:
| Wire | Read To | Resistance | DVA |
|---|---|---|---|
| Black/Yellow | Engine GND | 3250-3650 | 180V or more |
| Black/White | Engine GND | 200-250 | 25V or more |
- Check the trigger resistance and output:
| Wire | Read To | Resistance | DVA |
|---|---|---|---|
| Brown/Yellow | Brown/White | 750-1400 | 4V or more |
| Brown/Yellow | Engine GND | Open | 1V or more |
| Brown/White | Engine GND | Open | 1V or more |
No Fire on One Cylinder
- Check the DVA output on the green wires from the switch box while connected to the ignition coils. Check the reading on the switch box terminal and on the ignition coil terminal. You should have at least 150V or more at both places. If the reading is low on one cylinder, disconnect the green wire from that ignition coil and reconnect it to a load resistor, then retest. If the reading is now good, the ignition coil is likely bad. If it remains low, the power pack is likely bad.
1994–1998 Models
(With the 18495 Switch Box)
(With the 18495 Switch Box)
No Fire At All
- Disconnect the black/yellow kill wire and retest. If the ignition system now fires, the kill circuit has a problem.
- Check the stator resistance and DVA output:
| Wire | Read To | Resistance | DVA |
|---|---|---|---|
| Blue | Black | 3250-3650 | 180V or more |
| Red | Black | 200-250 | 25V or more |
Note: This system uses a timing advance circuit inside the switch box to control timing. The black stator wire is not tied directly to ground inside the pack.
- Check the trigger resistance and output:
| Wire | Read To | Resistance | DVA |
|---|---|---|---|
| Brown/Yellow | Brown/White | 750-1400 | 4V or more |
| Brown/Yellow | Engine GND | Open | 1V or more |
| Brown/White | Engine GND | Open | 1V or more |
No Fire on One Cylinder
- Check the DVA output on the green wires from the switch box while connected to the ignition coils. Check the reading on the switch box terminal and on the ignition coil terminal. You should have at least 150V or more at both places. If the reading is low on one cylinder, disconnect the green wire from that ignition coil and reconnect it to a load resistor, then retest. If the reading is now good, the ignition coil is likely bad. If it remains low, the power pack is likely bad.