Maik

[Maik]

Guys, thank you all for your time and your ideas.

I think I finally solved the problem.

After following the wiring diagram and measuring everything I could, I became more and more suspicious of the mysterious “filter” (which I believe is some kind of diode pack).

For anyone who might have the same issue one day, here’s what I did:

I bypassed the “filter”. I never managed to find it physically, so I assume it’s hidden somewhere inside the wiring harness.

I cut the YR wire at the connector and ran a new wire directly to the YR wire at the starter switch.

It works like a charm, and all the safety functions (clutch switch, etc.) are still working as intended.

I also installed a diode in the new wire to prevent voltage from feeding back into the circuit. I’m not even sure it’s necessary, but I preferred to be on the safe side and protect the ECU.

Maybe this will help someone else in the future.

Thanks again!

[Maik]

Thanks for your suggestion!

I’m pretty confident the battery is not the problem. It’s only about two years old, and just to be sure I also connected a car battery while testing. The behavior was exactly the same.

I also think the starter relay itself is OK.

If I manually connect the GR wire to battery negative and the YR wire to battery positive, the relay clicks immediately. If the starter motor is connected at the same time (I disconnected it for some of the tests), the starter cranks and the engine starts right away.

Maybe my understanding is wrong, but I would expect these control wires to receive the correct voltage during the normal starting sequence. I believe YR is the positive side of the relay coil.

To me it looks like the relay simply isn’t being driven by the bike’s wiring.

That’s why I’m currently thinking about a broken wire, a bad connector, or something else in the control circuit.

The only other possibility I can think of would be the ECU. But that doesn’t really make sense to me. Why would the ECU suddenly fail only in this single function? During the start attempt the fuel pump primes again, so the ECU is clearly alive and responding. The crankshaft position sensor must also be working, because once I bypass the relay the engine starts and runs normally.

So, at the moment, I’m leaning much more towards a wiring issue than a faulty ECU.

[Author]

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