"1990 Medium Truck C5H, C6H, C7H Models Electrical Diagrams and Diagnosis Manual" Written for GMC dealership mechanics, this factory-published original wiring diagram shows you how to follow the wiring from bumper-to-bumper. It will help you understand connector configurations, and locate and identify circuits, relays, and grounds. You will not find these wiring diagrams in the factory shop manual. Wiring diagrams are black and white, but they frequently have color codes printed on each line of the diagram that represents a wire. This manual covers all 1990 GMC TopKick and Chevy Kodiak Medium Duty Truck models including C5H, C6H, & C7H. This book is in good, used condition, measures 17.25" x 11" and is 0.5" thick. Buy now for the best electrical information available.