Cerbera wipers ECU — schematic reference

This page documents the TVR Cerbera wipers ECU — the small relay box that drives the windscreen wiper motor (slow, fast and park) and the washer pump. The information below is reconstructed from a KiCad schematic of the unit and is intended as a reference for owners diagnosing wiper faults or building a replacement board.

The design is purely electromechanical: four relays, six diodes and a 17-way connector. There is no microcontroller, no firmware, and the stalk switch directly drives the relay coils.

Applies to

TVR Cerbera (factory wipers ECU with 17-way harness connector).

Component overview

Ref	Part	Type	Role
K1	Omron G2RL-1	SPDT, 12 A	Washer pump
K2	Finder 40.52	DPDT, 10 A	Wiper speed 2 (fast)
K3	Finder 40.52	DPDT, 10 A	Wiper speed 1 (slow)
K4	Finder 40.52	DPDT, 10 A	Park / self-hold
D1–D4	1N4001	Diode	Coil flyback (one per relay)
D5, D6	1N4001	Diode	Steering diodes in park circuit
J1	TVR 17-way	Connector	Harness interface

J1 — 17-way harness connector

The connector is arranged in two rows: an A side (left) and a B side (right). Note that the factory numbering skips A5 — this matches the loom and is not an error.

Pin	Label	Signal	Direction	Function
1	A1	—	—	Not used
2	A2	Park switch	Input	Feedback from wiper motor park cam
3	A3	Speed 1 drive	Output	Motor supply, slow speed
4	A4	Ignition	Input	12 V when ignition on (park hold enable)
5	A6	Speed 2 drive	Output	Motor supply, fast speed
6	A7	—	—	Not used
7	A8	—	—	Not used
8	A9	Washer drive	Output	Washer pump supply
9	B1	Wiper 2 signal	Input	Stalk request — fast
10	B2	Wiper 1 signal	Input	Stalk request — slow
11	B3	—	—	Not used
12	B4	—	—	Not used
13	B5	—	—	Not used
14	B6	—	—	Not used
15	B7	—	—	Not used
16	B8	—	—	Not used
17	B9	Washer signal	Input	Stalk request — wash

How the circuit works

Slow and fast wipe (K3 and K2)

The stalk produces a switched 12 V on either Wiper 1 signal (B2) or Wiper 2 signal (B1). That signal energises the corresponding relay coil — K3 for slow, K2 for fast — and the relay contacts pass battery 12 V out to the motor via Speed 1 drive (A3) or Speed 2 drive (A6).

Both K2 and K3 are DPDT, so both poles of the motor circuit are switched together. That means selecting fast cleanly disconnects the slow path (and vice versa) without back-feeding through the motor windings.

Each coil has a 1N4001 diode wired across it in reverse bias (cathode to the +12 V end) to absorb the inductive kick when the coil drops out.

Washer (K1)

Pulling the stalk to wash sends 12 V to Washer signal (B9), which energises K1. Its normally-open contact connects 12 V to Washer drive (A9) and the pump runs for as long as the stalk is held. SPDT is sufficient here — the pump is a simple on/off load. D1 provides flyback protection.

Park circuit (K4 with D5 and D6)

The park circuit makes the blades always return to the rest position when you switch the wipers off, instead of stopping mid-screen. It uses:

K4 (DPDT relay) as the hold relay
Park switch (A2) — a cam-operated contact inside the wiper motor that is closed everywhere except at the park position
Ignition (A4) — to enable the hold path only when the ignition is on
D5 and D6 — steering diodes that isolate the park hold path from the speed-drive paths so current cannot back-feed between them

Sequence of operation:

With wipers running, K2 or K3 is energised and the motor is being driven directly.
When the stalk is switched off, K2/K3 drop out — but the motor is still away from the park position, so the park switch is closed.
The closed park switch, combined with the ignition supply, keeps K4 energised. K4’s contacts route 12 V to the slow-speed motor input, so the motor keeps turning.
The cam reaches the park position, the park switch opens, K4 drops out, and the motor stops with the blades parked.

D5 is fitted reversed relative to D6 — that is correct for a two-diode steering pair, not a mistake. D4 across K4’s coil is the usual flyback diode.

Power and coil current

Supply	Source pin	Used for
12 V switched	Stalk signals (B1, B2, B9)	Relay coil energisation
12 V motor feed	Via relay contacts to A3 / A6	Wiper motor
12 V pump feed	Via K1 to A9	Washer pump
Ignition sense	A4	Park hold enable

There are no driver transistors — the stalk contacts carry the coil current directly. Approximate coil currents at 12 V:

Relay	Coil current (approx.)
Omron G2RL-1 (K1)	~100 mA
Finder 40.52 (K2, K3, K4)	~135 mA each

Worst case (several relays energised together) is around 400–500 mA flowing through the stalk contacts. Worth keeping in mind when diagnosing intermittent wipe operation caused by tired stalk contacts.

Diagnostic notes

No slow wipe, fast works (or vice versa): suspect the corresponding relay (K3 or K2), its coil-drive wire from the stalk, or the 1N4001 across that coil failing short.
Wipers stop mid-screen instead of parking: look at K4, the park switch feed on A2, and the ignition feed on A4. A failed D5 or D6 can also break the parking logic.
Washer dead but wipers fine: K1, D1, the B9 stalk feed, or the pump itself.
Nothing works at all: check the ignition feed on A4 and the supply paths feeding the relay common contacts before condemning the ECU.

Always verify pin functions on your own car before cutting into the loom — colour codes and connector orientation should be cross-checked against the Cerbera wiring diagrams.

Safety note

The wiper and washer circuits are safety-related. If you rebuild or replace this ECU, fit inline fusing on the motor and pump supply lines (A3, A6 and A9) and verify all flyback diodes are present and the correct way round before reconnecting the harness.

Compiled from a KiCad schematic upload of the Cerbera wipers ECU — always verify against the original car and wiring diagrams before relying on it.