Mercury - Manual-Install - 90-891547051. The Mercury Manual-Install - 90-891547051 is an official installation manual designed to guide you through the proper setup of Mercury outboard and marine engine systems. Whether you're outfitting a new boat or replacing a critical component, this manual provides step-by-step directions to ensure accuracy, safety, and peak system performance.. Key Features. Official Mercury Documentation - Factory-issued guidance ensures proper installation. Illustrated I