This document summarizes key aspects of marine electrical systems including: 1) Electrical safety hazards such as electric shock, overcurrent, and thermal hazards. 2) Common electrical instruments for measurement such as ammeters, voltmeters, and ohmmeters. 3) Procedures for testing continuity, resistance, and insulation of wiring, cables, and equipment. 4) Types of tests including current injection, pressure, and earthling testing to evaluate electrical system integrity and performance.