03 Hardware
Power architecture
Two 12 V feeds, main relay, grounds and why they are not interchangeable.
7 min readUpdated 2026-08
Race Core has two 12 V domains and two ground domains. Mixing them is the most common install mistake.
+12 V
| Pin | Name | What it powers |
|---|---|---|
| B18 | +12 V Raw | MCU, logic, 5 V sensor supplies, USB. This is the ECU’s brain power. |
| B23 | +12 V MR | ETB H-bridges and high-side drivers. Feed this from the EFI main relay output. |
Two legal ways to run the main relay:
- ECU-controlled (preferred): ignition switch powers B18 only. A low-side (typically LS 13) grounds the main-relay coil. Relay output feeds injectors, coils’ 12 V, pump relay, and B23. The ECU is alive before the loads, so it can sequence pump prime and ETB home.
- Ignition-controlled: ignition switch drives the main relay. Relay output feeds B18 and B23 together (plus injector 12 V). Simpler, but the relay clicks even if the ECU is dead, and you lose prime sequencing.
Grounds
| Domain | Pins | Goes to |
|---|---|---|
| Power GND | A17, A18, A24, B19 | Engine block or a dedicated 8 mm ECU stud with a short run to the battery negative. |
| Sensor GND | C1–C8, C23 | Sensor ground pins only. Star at the ECU. Never the block. |
Sensor supplies
- Two independent 5 V rails, 150 mA each, short-circuit protected. MAP + TPS + PPS usually live on 5 V Sens 1; a second TPS or pressure sensors on 5 V Sens 2 so a short on one rail does not kill the other.
- Protected 12 V out on C11/C12 for Hall sensors that want 12 V.
- Do not power a wideband heater from the 5 V rail. Heaters are 12 V and several amps — they belong on the main relay with their own fuse.