This is the original wiring diagram printed by GM for dealer mechanics. You can follow the wiring in your truck from bumper-to-bumper. It will help you to understand connector configurations, and locate & identify circuits, relays, and grounds. Although the schematic is in black and white, the color of each wire is noted. You will not find this diagram in your shop manual. The schematic measures 8.5" x 11" when folded up, and opens up to 11" by 38". The diagram pictured is an example of this type when folded, but is not the actual diagram for your vehicle. Buy now for the best electrical repair info - the factory wiring diagram.
1978 Truck Wiring Diagrams Medium and Heavy Duty Models MD-16767
This item is original.
11.00 x 8.50 x 0.10 inches
This book covers 1978 GMC Brigadier and Chevrolet Bruin also known as J-9, equipped with the Cummins NTC 250, 290, or 350 diesel engine. See my other items other engines. To verify that this is the correct diagram for your truck, you can check your VIN code. The 2nd digit should be a C for the heavy duty steel conventional cab, the 3rd digit should be a C for the Cummins engine, and the 6th digit should be an to indicate the 1978 model year.
1978 Chevrolet 70-80 Series Heavy Duty
1978 GMC Series 7500-9500
1978 Chevrolet 70-80 Series Heavy Duty 1978 GMC Series 7500-9500