The number "1" on the distributor cap indicates the location of the terminal that fires the first cylinder *in the firing order*. The firing order for a 351 Windsor (the most common 351 in those trucks) is typically 1-5-4-2-6-3-7-8. A 351 Cleveland has a different firing order.
To find the correct wiring:
1. Identify your engine type: Is it a 351 Windsor or a 351 Cleveland? This is crucial because they have different firing orders. The engine block itself should have casting numbers to help identify it.
2. Find a firing order diagram: Look up a diagram for your specific engine type in a repair manual (Haynes or Chilton are good options), online forums dedicated to Ford trucks, or a reliable automotive website.
3. Locate cylinder #1: This is usually marked on the engine block near the front of the engine.
4. Follow the firing order: Using the diagram, connect the spark plug wire from the "1" terminal on the distributor cap to the spark plug in cylinder #1. Then, continue following the firing order to connect the remaining wires.
In short: Don't just go by the number on the cap; use the firing order for your specific engine.
