[SOLVED] Diagnose my starter problem please

[Fazerider]

You are correct, if the voltage between the starter relay output and the negative terminal of the battery is 11.89v and the starter motor doesn't turn, that tells you that the relay is not the problem.
So you have poor continuity between the relay and starter.
There are other possibilities: poor grounding of the engine or the starter itself needing a clean and new brushes, but if the thing spins reliably when you put a jump lead to it that makes these less likely.


Unfazed: sorry to disagree with you, but the voltage measurement is very useful. You can't have a 12v output from the relay with the motor not turning and blame the relay!