Model Condition Price Qty  
MD11878 Very Good $29.00
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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.
General Motors
"Cab, Engine and Chassis Wiring - HI/JI-9003; HI/JI-9500 - MD-11878"
1
Included
This item is original.
11.00 x 8.50 x 0.10 inches
MD11878
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This book covers mid-1975 GMC and Chevrolet 90, 9000, 9500, 95 Conventional models also known as HI or JI, equipped with the 6-71 diesel engine. See my other items for other engines. To verify that this is the correct diagram for your truck, you can check your VIN code. The 2nd digit should be an H or a J for the heavy duty steel conventional cab, the 3rd digit should be an I for the 6-71 engine, and the 6th digit should be a 5 to indicate the 1975 model year.

To find out if yours is a mid-year model (built after March 1, 1975), check the last six digits of the VIN, which should be larger than 590000 for GMC or larger than 140000 for Chevrolet. See the 1974-1975 diagram if the last six digits are smaller.
1975 Chevrolet 70-90 Series Heavy Duty
1975 GMC Series 7500-9500
1975 Chevrolet 70-90 Series Heavy Duty 1975 GMC Series 7500-9500