Hello,

I'm hoping someone can point me in the right direction.  

K100RS 1983.

Went out for a spin when the charge light came on brightly.  Bike seemed to be running fine, but I headed straight home.  The neutral light didn't work though headlights, indicators and horn did.

Turned the bike off when I got home but when I turned it back on there is no neutral light and the bike wont turn over even when I pull the clutch in. 

The bike has been showing a dim charge light off and on for some time and after checking the forum this appears to be fairly normal.

The bike has stalled a couple of times when approaching traffic lights but started on the button no issues.

There is a new battery fitted, which I've checked and seems to hold it's charge fine.

So far:-
Checked the battery connections - cleaned.
Checked the earth point under the tank - cleaned.
Ignition switch seems to be ok
Kill switch ok
Clutch switch ok
Took starter motor off and got rid of the worst of the dust/debris inside.
Took the Alternator brushes out and these seem ok for length.
Took the clocks off and checked the Neutral bulb, 12v gives a nice bright light.
When turning the ignition on there is a relay that clicks in.

Hopefully someone can help, bike is laid up and were seeing some great days to be out for a ride.

Thanks in advance.

Shug

Welcome shug!

About cranking problems....check fuse #1.....and if power is present with ignition on.

I would guess that you have a short to ground in the fuse #1 circuit,
which also have caused the charge warning light to illuminate.

Hello Inge K,

Thanks for your welcome and quick response.

Yes I have 12v at fuse 1.

Shug

Is the neutral lamp the only warning/signal lamp which don't function?

No, the choke light and the Brake check light aren't coming on either.

The clock cluster background lights, Indicator Warning and high beam warning lights all light up.

And oil pressure?

Hello, sorry, No the oil pressure warning light isn't on either.

Just remembered another issue whilst it was running.  

The speedo needle and possibly the tacho needles dropped onto the stop ie reading zero whilst riding.  The Speedo needle had been a bit jumpy for a short period.

All the warning lamps that don't function (BMU, choke, oil pressure, charge) is powered
from fuse #1.................also neutral lamp, clutch switch -/- starter button.

All this is still pointing to the fuse #1 circuit, I suggest that you try to change the fuse.


.....another sign is no brake light, also powered by fuse #1.



About your last post...speedo and tacho is also powered from fuse #1.

Brilliant!  Swapped fuse 1 and bingo the warning lights all come on.

But! pushing the starter button doesn't turn it over.  I can hear/feel a relay kicking in and out with the button push, possibly the load shed.  I'm getting about 11v at the starter relay when pushing the starter button but the relay doesn't operate.  I'll do some checking to see why I'm getting 1-2v drop to the relay, hopefully a bad connection.

Taking a jumper from the battery + to the Relay switched input doesn't trigger it either.

Could the starter relay be faulty and that's what caused the fuse to go

Measure if you got ground at the connector to the negative side of the coil.

780 ohm resistance to the battery -ve terminal.

starter brushes  ?

The starter relay coil is grounded through the ignition ECU (under the tank).
This problem shows up now and then (so you're not the first, but that don't help...)
usually a new ECU is needed...but check the multiconnector and clean (DeoxIT)
if needed, and check that the ECU got good ground.

Some have also connected the negative side of the starter relay directly to ground
when this problem have arised.

 Firstly, thanks Inge K, you've been a great help.  I was struggling to get my head around the problem and you're guidance has been quick, logical and accurate.

Had a look at the ECU connector which seems fairly clean.

Jumped from the ground connector on the starter relay to the battery -ve terminal and Bingo the bike turns as it should.

I'll probably rig a direct earth until I get a replacement ECU.  I'm guessing it's not a viable repair, bear in mind my first class fuse checking abilities LOL

Thanks again for your help.

onya inge !
a good find shug ...

Well done boys.  I love this forum for the help you get. No one bitches everyone just gets on with the job.  GREAT GREAT GREAT

Top notch troubleshooting Inge it does not get better than that for deduction.
Regards,
K-BIKE

Replacement ECU arrived, fitted, Warning lamps came on, bike started, the fuse didn't blow again.  So out for a spin, about 30 miles later no repeat.  Though I did have 1 cut out when pulling up which was a groan moment.  Think I have multiple issues I need to sort.

Anyway, as I'm an inquisitive bgr! and I had a defunkt ECU which was surplus so I opened it up for a look see.  

The PCB tracks are all lifting from the board, not good, and probably renders the board useless (at least for my limited skill level)

Same problem as I had last year.

I also replaced the EC but became convinced the problem was actually the connectors at the ECU rather than inside the unit. The trouble is that you never know if the problem is a faulty sensor somewhere, a bad connection between the sensor and the ECU, or a bad connection into the ECU. That's before you suspect the ECU itself.

I never tested the unit because it was more convenient and cheaper to buy another from Motorworks rather than getting mine tested. Mine did look perfect inside. I had already swapped over the starter and load shed relay to no avail.

Welcome too. Cornwall is nice.