Coils · igniter · ECU outputs

Ignition coil wiring diagram

There are two kinds of ignition coil, and they are wired differently. Connect one the way the other is meant to be wired and you get no spark — or a burned ECU output. Here is how to tell them apart.

Open the editor · ▶ Run the live demo

Plain coil (no igniter)

Terminal 15: +12 V from the ignition or the main relay, through a fuse.
Terminal 1: the primary’s negative end, switched to ground by an igniter or an ECU output built for coils.
Terminal 4: high voltage to the spark plug or the distributor.

Coil with a built-in igniter (“smart coil”)

+12 V: power through a fuse.
GND: a solid ground, usually to the engine.
IGT: a low-current logic signal from the ECU (typically 5 V) that tells the coil when to fire.

The classic mistake

A smart coil on an ECU output that switches to ground sees no logic signal and never fires; a plain coil on a logic output draws far more current than that output can give. WireForge checks the ECU output type against what is connected and warns.

See it in the ECU demo

Open the “ECU fuel injection” demo and drag the engine speed up.
Add an ignition coil device in the editor and wire it to an ECU ignition output.
Simulate: the ECU fires the coil in step with the crank signal; a mismatched output type shows a warning.

Questions

How do I know if my coil has an igniter?

Three or four pins (power, ground, signal, sometimes a feedback) usually means a built-in igniter; two low-voltage pins means a plain coil.

Can an ECU drive a plain coil directly?

Only through an output built for it (an igniter stage); a logic ignition output needs an external igniter.

Does the simulator model the spark?

No. It models the low-voltage side: power, ground, which output fires when, and whether the output suits the coil.

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