NEWHOW 3-Pack Ignition Coil 300-8M0077471 12V for Mercury Optimax

Key features

• 3-Pack 12V EFI/DFI Smart Ignition Coils — Replaces 300-8M0077471 / 8M0077471 Set of three direct aftermarket ECM-driven ignition driver coils​ for Mercury/Mariner OptiMax & EFI outboards. Each replaces Mercury 300-8M0077471, 8M0077471, 339-8M0077471​ and prior 879984T01, 879984T00, 879984A1, 339-879984T01/T00/A01, 300-879984T01, crossing Sierra 18-5158, CDI 184-0003, Recmar REC300-8M0077471. 12V, ~0.5-1.0Ω primary, ~5-15kΩ secondary, 20-40kV output, 2-pin plug + HT tower, epoxy black shell. Match old stamp 300-8M0077471 or 8M0077471​ before order.
• For Mercury OptiMax DFI 75-250HP & EFI 30-60HP (2002-Up) Engineered for OptiMax 75/80 Jet/90/115/125 DFI 3-cyl, OptiMax 200/225/250 DFI 3.0L, EFI 4S 30/40 3-cyl & 50/60 4-cyl, 2.5L/3.0L EFI 150-250, Pro XS 115-250, 225/250 XS, 300 XS, MerCruiser SCi 600-1200 / QC4V race​ (S/N 0T980000-Up on many OptiMax). 3 coils = complete set for 3-cyl OptiMax 75/90/115.
• Fixes P0300 Misfire, OptiMax Beeper, Hard Start & Flat Spot Resolves smart-coil faults: ECM throws P0301-P0303 single-cyl misfire, OptiMax alarm beeps 3× at idle, cold start needs 5+ cranks, no power above 3500rpm on one cyl. Internal driver IGBT fails or secondary opens. New coil restores 20-40kV under ECM dwell. Test old: primary 0.5-1.0Ω across 2 pins, secondary 5-15kΩ pin-to-boot; open = dead.
• Bolt to Head Coil Seat, Dielectric Grease on Plug Disconnect negative battery, unplug 2-pin, remove 1× 5mm bolt per coil, lift old coil off plug, seat new coil, torque 35 in-lb, reconnect plug, apply dielectric grease to HT tower before pushing boot on. Critical: OptiMax coils sit low on head — water intrusion kills them; reuse original boot or fit new OEM-style boot. Do not swap coil positions randomly on DFI (physical cyl mapping must stay).
• Confirm 2-Pin + HT Tower + EFI/DFI Before Ordering This is the ECM-driven smart coil with 2-pin control plug + 1 HT tower​ for OptiMax DFI & EFI 4S/2S engines (2002-Up). Before ordering, photo your old coil and confirm (1) two control pins, (2) one high-tension tower, (3) black epoxy housing, (4) stamp reads 300-8M0077471 or 8M0077471. Engine must be EFI/DFI (OptiMax or EFI 4S/2S)​ — carbureted models use a different ignition architecture and are not covered by this coil. If old coil has 4 pins or no HT tower, it is a different generation and will not fit.

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