Power, grounds & main relay

How the latch works

On key-on the ECU grounds E4, the relay closes, M4 comes alive, and firmware holds the relay until it has finished writing to flash on shutdown. E4 is not a TunerStudio-assignable output.

• L4Key-on 12 V
• E4Main relay control
• M412 V from main relay
• M3Power ground
• L3Power ground

Relay pinout (standard 5-pin automotive)

• 30 — constant battery 12 V, fused 25–30 A close to the battery.
• 87 — switched 12 V out to M4, injectors, coils, VVT, idle, sensor 12 V if used.
• 86 — relay coil to ignition-switched 12 V (same feed as L4 is fine).
• 85 — relay coil to ECU E4 (low-side).
• 87a — unused.

Grounds

M3 and L3 are power ground. Run both, 2.0 mm² or thicker, to a sanded boss on the block or heads — not a painted seat-belt bolt. H4 and G4 are analog ground. Sensor grounds stay in that star and only meet chassis inside the ECU.

Minimum fuse map

• Battery → relay 30: 25–30 A.
• Key-on → L4 and relay 86: 5 A.
• Relay 87 → injectors / injector driver: 10 A (4-cyl) to 20 A (8-cyl batch).
• Relay 87 → coil +12 V: 10–15 A.
• Fuel pump (via D2 relay): 15–20 A on the pump side, 5 A on the coil side.