What is the spark plug wiring diagram for a gmc 366 engine?

There isn't a single, universal spark plug wiring diagram for a GMC 366 engine. The firing order and therefore the wiring will vary depending on the specific year, application (truck, bus, marine, etc.), and even the ignition system used (points, electronic ignition, etc.).

To find the correct wiring diagram, you need to provide more specifics:

* Year of the engine: The design and ignition system changed over the years.

* Engine serial number: This will pinpoint the exact configuration.

* Application: What vehicle or equipment did this engine power?

Once you have this information, you can:

* Consult a repair manual: A factory service manual for your specific GMC 366 engine will have the correct wiring diagram and firing order. This is the most reliable source.

* Use an online parts catalog: Some online parts providers (like those specializing in classic truck parts) may have diagrams available if you input the engine's details.

* Look for a tag or sticker on the engine: Sometimes the firing order is printed directly on the engine itself.

Without this specific information, any diagram provided would be unreliable and potentially damaging to your engine. Improper wiring can lead to misfires, damage to the ignition system, and even engine damage. Always use a reliable source for this critical information.