Rectifier (aka Voltage Regulator). Most commonly used for (but not limited to) 400cc ATVs such as the Jianshe JS400 Mountain Lion as well as many other clones, rebrands and similar displacement machines.
Common Jianshe model name is primarily listed as "Jianshe JS400", "Jianshe JS400ATV", "Jianshe 400cc ATV", "Jianshe 400cc 4x4" and "Jianshe 400cc Mountain Lion". Common listed Jianshe JS400 rectifier / voltage regulator part number is F3-D40000-0 and listed as "RECTIFICATION REGULATOR" in their parts lists. Also applies to some variations of Jianshe 400cc Go karts, buggies, UTVs and other products.
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