What is a relay on a Rotax BRP engine?
The relay is an essential electrical component of your Sea-Doo jet ski or WILLIAMS tender's electrical system equipped with a Rotax BRP engine. It acts as an electronically controlled switch: it receives a low-current signal (from the dashboard, starter, or ECU) and switches a high-power circuit accordingly.
On Rotax ACE 903, 1503, and 1603 engines, there are primarily two types of relays:
- Starter Relay (Starter Solenoid): It powers the electric starter when the engine is started.
- 12V / 35A Power Relay: It manages the power supply to secondary circuits (fuel pump, accessories, ECU).
A faulty relay can completely immobilize your watercraft, even if the rest of the electrical system is in perfect condition.
Why do relays wear out?
Relays are subjected to severe stresses in a marine environment:
- Humidity and salt: Corrosion of internal contacts is the primary cause of failure.
- Vibrations: Repeated shocks weaken internal solders and contacts.
- Thermal cycles: Temperature variations between sailing sessions accelerate component aging.
- Electrical overloads: A short circuit or overcurrent can burn out contacts in seconds.
In a marine environment, the lifespan of a relay is generally shorter than that of an equivalent automotive relay. Regular preventive maintenance is therefore strongly recommended.
Symptoms of a Faulty Relay
Recognizing the signs of a relay nearing the end of its life will allow you to intervene before a complete breakdown at sea. Here are the most common symptoms:
Starter Relay (Solenoid)
- Engine won't start: You turn the key or press the start button, but nothing happens—no starter noise.
- A sharp click without starting: The solenoid activates (you hear a "click"), but the starter doesn't turn.
- Intermittent starting: The engine sometimes starts, but not always, for no apparent reason.
- Burning smell: Sign of a burned contact or internal overheating.
12V / 35A Power Relay
- Loss of power to accessories: Dashboard instruments, fuel pump, or ECU no longer power up correctly.
- Random engine cuts: The engine stops for no reason while sailing.
- Fault light on: An electrical fault code may appear on the dashboard.
- Difficulty starting when hot: The relay works when cold but fails once the engine is hot.
How to Diagnose a Faulty Relay?
Before replacing a relay, it's possible to perform a quick diagnosis with a multimeter:
- Check the voltage at the relay terminals: You should measure 12V at the input when the control circuit is activated.
- Test output continuity: When the relay is activated, the resistance between the power terminals should be close to 0 Ω.
- Listen to the relay: A healthy relay emits a clear "click" when powered. A silent relay or one that clicks without switching is faulty.
- Visually inspect the contacts: Corrosion, blackening, or burn marks are obvious signs of failure.
In practice, and if you don't have tools at hand, on ROTAX ACE903, 1503, or 1603 engines, you can quickly identify a faulty relay by opening the engine's fuse box (a black plastic box on the engine's harness similar to the photo below) and swapping the two small relays inside. If the nature of the fault changes, it means one of the two relays is faulty.
If the relay does not switch correctly or if the contacts are oxidized, replacement is necessary.
When to Replace Relays?
We recommend replacing relays in the following situations:
- Every 3 to 5 years for preventive maintenance, even in the absence of symptoms.
- As soon as any of the symptoms described above appear.
- After an electrical overload or a short circuit on the affected circuit.
- During a complete overhaul of the electrical system (winterizing, spring restart).
Which Relay to Choose for Your Sea-Doo or WILLIAMS?
It is imperative to use relays that comply with OEM BRP specifications to ensure the reliability and safety of your watercraft. Here are the original references, available on rotaxtenderparts.com:
- 35A/12VDC Relay for Rotax SEADOO & WILLIAMS Engine: The standard power relay for Rotax ACE engines. Compatible with Sea-Doo Spark, WILLIAMS Minijet, Sportjet, and Turbojet. --- (Replace both relays at the same time) ---
- SEADOO & WILLIAMS Starter Solenoid Relay – Ref. 278000513: The original BRP starter solenoid, compatible with the main OEM references (278002347, 278001802, 278001766).
- 12VDC SEADOO & WILLIAMS Power Relay – BRP Rotax Ref. 278003012: 12VDC power relay OEM reference 278003012, for secondary circuits.
Compatibility
The relays referenced above are compatible with the following models:
- Sea-Doo Spark (Rotax ACE 903 engine)
- Sea-Doo Spark Trixx
- WILLIAMS Minijet 280
- WILLIAMS Sportjet 345 / 395
- WILLIAMS Turbojet 325 / 435
For other Sea-Doo models (GTI, GTX, RXT, Wake) equipped with Rotax 1503 or 1603 engines, check the OEM reference on your original relay before ordering.
Conclusion
The relay is an often-neglected wear part, but its failure can immobilize your jet ski or tender at the worst possible moment. Regular preventive replacement, combined with visual inspection during each service, guarantees optimal reliability when sailing.
Find all our Sea-Doo and WILLIAMS compatible relays on rotaxtenderparts.com, with immediately available OEM BRP references.
