Where is the number 1 on a distributor cap?
The terminal labeled 1 on a distributor cap is the spark plug connection for cylinder number 1, as defined by the engine’s firing order. Its physical location varies by cap design and manufacturer, so you should look for a “1” mark on the cap or refer to the vehicle’s service manual for the exact layout.
Understanding cap numbering
Distributor caps route high-voltage sparks from the rotor to each spark plug. Terminal numbering is not standardized across all brands, so you must rely on markings, diagrams, or firing-order information to map terminals to cylinders.
Where the label might appear
Many caps have numbers stamped around the terminals, or a diagram inside the cap lid showing the cylinder-to-terminal mapping according to the firing order.
How to identify the #1 terminal on your cap
Before handling ignition components, ensure the engine is off and the battery is disconnected. Then determine your engine’s cylinder 1 location and confirm the cap’s layout using one of these methods.
Use these steps to locate the #1 terminal on your distributor cap:
- Inspect for a stamped “1” near a terminal or a small schematic labeling the terminals around the cap.
- Check the service manual or a factory diagram for your exact engine, since firing order and cap layout differ among four-, six-, and eight-cylinder engines and between inline vs. V configurations.
- If there are no markings, rotate the engine to the compression stroke of cylinder 1 (top dead center) and observe where the rotor points; the terminal aligned with the rotor at that moment is the #1 terminal.
- Cross-check by mapping the remaining wires to their cylinders according to the firing order and ensuring the connections match the cap’s layout.
In short, the #1 terminal is the spark lead for cylinder #1, identified by cap markings or by rotor position aligned with the engine’s firing order. If there are no markings, rely on diagrams and manual mapping.
Note: On modern cars, some engines use distributorless ignition systems or coil-on-plug designs, which do not have a traditional distributor cap or numbered terminals. In those cases, this guidance does not apply.
Summary
The #1 terminal on a distributor cap is the spark connection for cylinder 1, but its exact position depends on the cap design and the engine’s firing order. Look for a marked “1” on the cap or consult the service manual for your vehicle. If markings are absent, determine the terminal by rotor alignment at cylinder 1’s TDC and verify against the firing order. When in doubt, seek professional assistance.
