Mercury 25 EFI Service Manual page 99

2. Remove the ignition coil high tension lead from the spark plug.
3. Check the resistance of the coil primary windings to engine ground. Replace the ignition coil if not within specification.
DMT 2004 Digital Multimeter
Red
Coil primary lead
4. Hold the high tension lead and rotate the spark plug cap counterclockwise. Remove the spark plug cap from the spark plug
high tension wire.
5. Measure the resistance of the ignition coil secondary winding to engine ground. Replace the ignition coil if not within
specification.
Coil high tension lead
90-8M0105568 eng MARCH 2016
a
b
c
9951
a
Meter Test Leads
Coil mounting bolt
a
a -
b -
b
9954
Meter Test Leads
Red
a - Coil high tension lead
b - Ignition coil
c - Ignition coil harness connector
a - Engine ground (coil mounting bolt)
b - Coil primary lead
b
9952
Black
Engine ground (coil mounting bolt)
Coil secondary winding (coil high tension lead)
Black
Engine ground
© 2016 Mercury Marine
91‑892647A01
Meter Scale
Auto range
Meter Scale
Auto range
Ignition
Reading (Ω)
0.17 ‑ 0.23
Reading (Ω)
3.3 ‑ 4.9k
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