Cylinder Numbering: Chevrolet small-block V8s are numbered sequentially from the front of the engine, driver's side (left) to the passenger's side (right).
* Passenger side (right): Cylinders 1, 3, 5, 7
* Driver's side (left): Cylinders 2, 4, 6, 8
Distributor Cap Wire Order: The distributor cap wires will correspond to the firing order. However, there's no standard "clockwise" or "counterclockwise" arrangement. You *must* physically trace each wire from the spark plug to the distributor cap to determine the correct order on your specific distributor. There is no substitute for physically checking this. A mis-wired distributor cap will result in very poor engine performance or no running engine.
Important Considerations:
* Engine Size: This firing order is for the common small-block V8s (typically 305 or 350 cubic inch). If your truck has a different engine (e.g., a big-block V8 or an inline-6), the firing order will be different. You'll need to find a resource specific to your engine's specifications.
* Distributor Rotation: The distributor cap's wiring order is dependent on the direction of distributor rotation. In almost all GM vehicles, the distributor rotates counterclockwise. However, it's still important to double check the wiring by tracing the wires.
Recommendation: Obtain a shop manual for your specific year and model GMC High Sierra 15. This manual will provide diagrams showing the cylinder numbering, firing order, and distributor cap wiring. This is the most reliable way to ensure accuracy.
