Any advice would be appreciated please:
Issue as follows. had a couple of times now where the engine management light comes on and within a minute or so the motor cuts out. The battery at that point is flat. So when, after charging the battery, I run tests everything seems fine. The 3 white wires at the rectifier reads 24.2 Volts. The red wire to battery neg terminal reads 5.5V. With rectifier back in line, the battery terminals read 12.6 V (engine off), with engine on it reads 14.2V.

So, I'm wondering if one of the coils could fail when the motor is hot? someone with experience of this issue?

Hi
not knowing the bike some of this does not make sense to me:
Red wire to battery negative terminal??

If this is a standard three-phase voltage regulator/rectifier (3 white AC wires in 1 red DC wire out) this is the positive terminal to be connected with. Regulator needs ground as well, so usually there is a grounding cable from one regulator fastener to battery negative terminal (or black harness wire).

You could fit a 12V socket to the bike and plug in a voltmeter plug, so you can check what the voltage does while you ride. Ignition will cut out well below 11 volt usually.
Could be as simple as a bad battery.

Andy

Thanx Andy

Yes, pretty standard

If this is a standard three-phase voltage regulator/rectifier (3 white AC wires in 1 red DC wire out) this is the positive terminal to be connected with. Regulator needs ground as well, so usually there is a grounding cable from one regulator fastener to battery negative terminal (or black harness wire).

I would have thought that the voltmeter across that red terminal to battery neg would read around 12+ V. the 5.5V seems anomalous to me but auto electrics is not my strong point

Thing is I replaced battery just before last winter, so I was thinking it is unlikely but you may well be right and I should not ignore the obvious. I'll load test the battery