{"product_id":"sierra-18-5709-marine-rectifier-for-johnson-evinrude-outboard-replaces-omc-581778-fits-up-to-9-9-hp","title":"Sierra 18-5709 Marine Rectifier, Replaces OMC 581778, for Johnson\/Evinrude Outboard Motors 9.9-40 HP","description":"\u003cp\u003eThe Sierra 18-5709 is a marine rectifier built as a direct replacement for the charging system on Johnson\/Evinrude outboard motors. It converts the AC output from the outboard's alternator into DC current to keep the battery charged while running, a critical function for reliable starting and onboard electronics. The housing is constructed of metal and plastic with a white finish, and it uses an engine-mount design so it bolts into the same location as the original unit on gasoline outboard motors.\u003c\/p\u003e\u003cp\u003eThis rectifier is engineered as an equivalent to OMC part number 581778, giving boat owners a straightforward way to source a charging-system replacement without hunting for a discontinued OEM part. It is designed for outboards rated up to 9.9 horsepower and is also listed across a range of Johnson\/Evinrude engines from 9.9 HP through 40 HP, spanning multiple production years, including several 2-cylinder configurations. Every Sierra part is backed by Sierra's standard limited warranty, giving buyers confidence in fit and function.\u003c\/p\u003e\u003ch3\u003eSpecifications\u003c\/h3\u003e\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003eBrand:\u003c\/strong\u003e Sierra\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eManufacturer Part Number:\u003c\/strong\u003e 18-5709\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eCategory:\u003c\/strong\u003e Outboard Rectifier\/Regulator\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eMaterial:\u003c\/strong\u003e Metal, Plastic\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eColor:\u003c\/strong\u003e White\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eWeight:\u003c\/strong\u003e 0.16 pounds\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eEngine Type:\u003c\/strong\u003e Outboard Motor\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eFuel Type:\u003c\/strong\u003e Gasoline\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eMounting Type:\u003c\/strong\u003e Engine Mount\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eCompatible Engine Brand:\u003c\/strong\u003e Johnson\/Evinrude\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eOEM Cross Reference:\u003c\/strong\u003e OMC 581778\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch3\u003eFitment\u003c\/h3\u003e\u003cul\u003e\n\u003cli\u003e9.9, 15 HP, 1974-92\u003c\/li\u003e\n\u003cli\u003e20 HP, 1989-98\u003c\/li\u003e\n\u003cli\u003e25 HP (2 Cylinder), 1977-03\u003c\/li\u003e\n\u003cli\u003e28 HP, 1989-96\u003c\/li\u003e\n\u003cli\u003e30 HP (2 Cylinder), 1989-03\u003c\/li\u003e\n\u003cli\u003e35 HP (2 Cylinder), 1976-93\u003c\/li\u003e\n\u003cli\u003e40 HP, 1974-76, 1988-92\u003c\/li\u003e\n\u003c\/ul\u003e\u003ch3\u003eReplaces (OEM)\u003c\/h3\u003e\u003cul\u003e\u003cli\u003eOMC 581778\u003c\/li\u003e\u003c\/ul\u003e\u003ch3\u003eFrequently Asked Questions\u003c\/h3\u003e\u003cp\u003e\u003cstrong\u003eWhat does the Sierra 18-5709 rectifier do?\u003c\/strong\u003e It converts the AC current produced by a Johnson\/Evinrude outboard's alternator into DC current to charge the battery, which is essential for reliable starting and onboard electrical systems on the motor.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eIs the Sierra 18-5709 a direct replacement for OMC 581778?\u003c\/strong\u003e Yes, the 18-5709 is built as a replacement for OMC part number 581778 and mounts in the same engine location as the original rectifier.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhich outboard motors fit the Sierra 18-5709 rectifier?\u003c\/strong\u003e It fits Johnson\/Evinrude outboards including 9.9 and 15 HP (1974-92), 20 HP (1989-98), 25 HP 2-cylinder (1977-03), 28 HP (1989-96), 30 HP 2-cylinder (1989-03), 35 HP 2-cylinder (1976-93), and 40 HP (1974-76, 1988-92).\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhat is the 18-5709 rectifier made of?\u003c\/strong\u003e The housing is made of metal and plastic with a white finish, designed for engine-mount installation on gasoline outboard motors.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eHow much does the 18-5709 rectifier weigh?\u003c\/strong\u003e The Sierra 18-5709 rectifier weighs 0.16 pounds.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWill the 18-5709 fit a 9.9 HP Johnson outboard?\u003c\/strong\u003e Yes, the 18-5709 is listed for 9.9 and 15 HP Johnson\/Evinrude outboards from 1974-92.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eDoes the 18-5709 fit 25 HP two-cylinder Evinrude motors?\u003c\/strong\u003e Yes, it fits the 25 HP 2-cylinder Johnson\/Evinrude outboard covering model years 1977-03.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eIs the 18-5709 a genuine OEM part or an aftermarket replacement?\u003c\/strong\u003e The 18-5709 is a Sierra-manufactured replacement rectifier engineered as an equivalent to OEM part OMC 581778, not an original OMC-branded component.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eHow is the 18-5709 rectifier mounted?\u003c\/strong\u003e It uses an engine-mount design, installing directly onto the outboard motor in place of the original charging-system rectifier.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eDoes the Sierra 18-5709 come with a warranty?\u003c\/strong\u003e Yes, the 18-5709 rectifier is covered under Sierra's standard limited warranty.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWhat is included when I order the 18-5709?\u003c\/strong\u003e The order includes one Sierra 18-5709 rectifier unit for Johnson\/Evinrude outboard motors.\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eWill the 18-5709 fit a 40 HP Evinrude?\u003c\/strong\u003e Yes, the 18-5709 fits 40 HP Johnson\/Evinrude outboards from 1974-76 and 1988-92.\u003c\/p\u003e","brand":"Sierra","offers":[{"title":"Default Title","offer_id":48988229697755,"sku":"SIE-18-5709","price":41.57,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0839\/7586\/4539\/files\/SIE-18-5709_lg__72558.1558128793.500.750.jpg?v=1785188118","url":"https:\/\/www.goodvibesmarina.com\/products\/sierra-18-5709-marine-rectifier-for-johnson-evinrude-outboard-replaces-omc-581778-fits-up-to-9-9-hp","provider":"Good Vibes Marina","version":"1.0","type":"link"}