Cerbera indicator ECU — schematic reference
This page describes the indicator and hazard ECU fitted to the TVR Cerbera, based on a reverse-engineered KiCad schematic of the board. It is a small relay-logic module that takes inputs from the indicator stalk and hazard switch and routes the external flasher unit’s output to the left lamp, right lamp, or both. There is no microcontroller — the entire control logic is implemented with four SPDT relays and a handful of diodes, which makes it straightforward to diagnose with a multimeter.
The values below are taken from a community analysis of the schematic file. Verify against your own board before cutting wires — production hardware may differ from the captured schematic.
What the board does
Section titled “What the board does”The ECU sits between three things:
- The indicator stalk (left and right request lines).
- The hazard switch (a single active line).
- The external flasher unit (the oscillator that makes the bulbs blink).
When a turn is requested, the appropriate relay routes the flasher’s oscillating output to the matching lamp circuit. When hazards are requested, a fourth relay re-routes the same flasher output to both sides at once. A separate “flash power” relay gates the supply to the flasher unit itself, so it only oscillates when an indicator or hazard function is actually active.
Components on the board
Section titled “Components on the board”| Ref | Part | Role |
|---|---|---|
| K1 | Omron G2RL-1 (SPDT, 12 V coil) | Hazard relay — bridges left and right outputs |
| K2 | Omron G2RL-1 | Flash-power relay — enables the external flasher |
| K3 | Omron G2RL-1 | Left indicator relay |
| K4 | Omron G2RL-1 | Right indicator relay |
| D1–D4 | 1N4001 | Flyback diodes, one across each relay coil |
| D5, D6 | 1N4001 | Steering diodes isolating hazard from stalk inputs |
| J1 | 17-way TVR connector | Main harness interface |
The G2RL-1 is rated 12 A at 250 VAC on the contacts with a 12 V DC coil — comfortably above the load of a set of indicator bulbs.
Connector J1 — pin assignments
Section titled “Connector J1 — pin assignments”The 17-way connector is laid out in two rows. Not all positions are used; the table below lists only the connected pins.
A-row (signals in and out)
Section titled “A-row (signals in and out)”| Pin | Net | In/Out | Purpose |
|---|---|---|---|
| A1 | Right Indicator | Output | Switched feed to right indicator lamps |
| A2 | Flasher Input | Input | Oscillating signal returning from the flasher unit |
| A3 | Left Indicator | Output | Switched feed to left indicator lamps |
| A6 | Ignition | Input | Ignition-switched 12 V |
| A7 | Flash Power | Output | Gated 12 V feed to the external flasher unit |
| A8 | Battery | Input | Permanent 12 V |
| A9 | Hazard Signal | Input | Active signal from the hazard switch |
B-row (stalk inputs and earth)
Section titled “B-row (stalk inputs and earth)”| Pin | Net | In/Out | Purpose |
|---|---|---|---|
| B1 | Right Turn | Input | Right stalk request |
| B4 | Left Turn | Input | Left stalk request |
| B9 | Earth | — | Chassis/ground return |
Pins A4, A5, B2, B3, B5, B6, B7 and B8 are unused in this design.
How the logic works
Section titled “How the logic works”Right turn
Section titled “Right turn”- Stalk pulls B1 (Right Turn) active.
- K4’s coil energises from the ignition supply.
- K4 contacts connect A2 (Flasher Input) through to A1 (Right Indicator).
- The right-hand lamps flash at the flasher unit’s rate.
- D4 absorbs the coil back-EMF when the stalk returns to centre.
Left turn
Section titled “Left turn”Identical to the above but using B4 → K3 → A3, with D3 as the flyback diode.
Hazards
Section titled “Hazards”- Hazard switch pulls A9 (Hazard Signal) active.
- K1 energises and bridges the contact paths of K3 and K4, so the flasher signal reaches both A1 and A3 simultaneously.
- D5 and D6 block the hazard feed from back-driving B1 and B4, which would otherwise look like a stuck stalk to anything else watching those lines.
Flash-power gating (K2)
Section titled “Flash-power gating (K2)”K2 only closes — and so only powers the external flasher via A7 — when the ignition is on and either a turn or hazard request is present. This stops the flasher oscillator drawing current with everything off.
Protection summary
Section titled “Protection summary”| Concern | How it’s handled |
|---|---|
| Relay coil back-EMF | 1N4001 across each coil (D1–D4) |
| Hazard back-feeding stalk inputs | Steering diodes D5, D6 |
| Lamp inrush / contact wear | G2RL-1 rated 12 A — well above bulb current |
| Logic faults | None — passive relay logic, nothing to reprogram |
Diagnosis tips
Section titled “Diagnosis tips”- If one side fails to flash, suspect that side’s relay (K3 for left, K4 for right) or its driver line from the stalk.
- If hazards don’t work but normal indicators do, suspect K1, D5/D6, or the hazard switch feed on A9.
- If nothing flashes, check A6 (ignition), A8 (battery), B9 (earth) and the external flasher unit before condemning the board — K2 won’t energise without ignition.
- The relays are standard automotive parts and are easy to swap; sockets are not used on the original board, so de-soldering is required.
Caution
Section titled “Caution”This is a safety-related circuit — working indicators are a legal requirement. After any repair, confirm correct operation on both sides and in hazard mode, with the engine running, before driving on the road. If in doubt about the wiring at your car, verify continuity to the harness rather than trusting this reference.
Compiled from a community KiCad schematic analysis of the Cerbera indicator ECU — always verify against your own board and the car’s wiring before relying on it.