Curvy electrical oddness?

[Grant66]

Couple of weeks ago whilst out on a run the bike refused to start, slow turnover, just like the battery being flat. Bump started, need bike in the morning so just charged battery.
I know what your thinking, rec/reg.

Everything seemed fine after and daily commute, play out, all good. No further issues. Forgot about it.

Today, around the third stop of the day, starter turned slowly but bike started ok. Hmmmm, battery not charging again, bummer. next few stops, no problem battery seemed fully charged. Stopped to fill up, bike refuses to start. Get it bump started (ta Nemesis) and squirrel diagnosed rec/reg, as I suspected.

Battery charging so can't start bike yet, so took the rear cowl off and discovered:





What your looking at is the main earth connector from the battery isn't connected.



So how the chuffin' 'eck was it working at all? Aren't earthing problems weird.

Reg/rec could still be goosed though, guess I'll find out tomorrow.

Does that mean you won't be coming over?

[Grant66]

Might do, I'm hoping the rec/reg is OK, but I'll be surprised if it isn't dead.

I'll be doing some checking tomorrow when hopefully pressing the starter makes more noise than 'click'.

[Grant66]

Update: I'm surprised.

Reg/rec checks out OK at the moment, 14.2V at 5000rpm. 80V ac from the generator at 5000. So all looks good now. Battery charged and a clean bill of health reported from the charger.

After a long stare at the circuit diagram I can't see an alternative 0V path, volt meter agrees with me. How it worked I don't know.

good news, thought it was you who woke me up

Excellent. Was gonna suggest having a look at the wiring and had my tool kit with me but thought someone more mechanical minded would probably diagnose it. Anyway, that's just the bike's way of pleading for more attention

Sorry but no way is that your main battery earth (far too thin) - I bet you have a much better one also connected to the -ve of the battery to the bike frame.

That *could* be a return for the starter relay - so perhaps it has finally fallen out and gave you poor/no starter action.

[Grant66]

Originally Posted by JM2

Sorry but no way is that your main battery earth (far too thin) - I bet you have a much better one also connected to the -ve of the battery to the bike frame.

Obviously, you would expect a 2.5mm cable to power the starter motor. Its shown on the circuit diagram as the big earth symbol.

Originally Posted by JM2

That *could* be a return for the starter relay

Yes it is and everything else that else that isn't a starter motor (exception being the Stebel horn & Oil pressure switch which also use the frame as return).

The point was its been like this for a while. That connection must have been off for at least a couple of weeks (first occurrence), the bike has worked perfectly since then and as that connector was Ty-wrapped (with factory ty-wraps) in a position where it was physically impossible to make a connection it may have been like that for the last 10 years (since manufacture). It was certainly dirty (oxidised) enough to suggest a few years of disconnection.

Funnily enough, I had exactly the same symptoms: every now and then, it just wouldn't start. When it did start, lights would be flickering so badly, as if the battery was completely dead. Yet plugging in the optimate showed it was OK.

So I took off the panels to get to the rectifier, and guess what, voltages all OK.

Turns out the screw of the negative terminal on the battery had come undone and giving an intermittent connection. How I felt stupid not seeing it sooner (but how relieved it was a zero-cost fix).