I went out for a short ride yesterday and half an hour in, the engine died  and the red triangular warning lamp came on. 

My reaction was to press the rear brake pedal, which extinguished the red triangular light, and the power came back.

I initially thought that the  back brake had came on via the ABS, which is why I pressed the back brake pedal.
but then realised I had lost all power momentarily.

I rode for another half an hour, then whilst coasting to a stop light, the bike died again with the red triangular light coming on. 
I pressed the starter and she instantly fired up, and I got back home with any further problems.

Recent maintenance as follows.

1. 50 amp alternator and new motobatt  battery fitted.
    Battery charge indicator bulb then  flickered occasionally for 50 miles or so and steady after with a good            charging  rate
    ABS lamps began to stay on now and again after operating both brakes, so swapped ABS brain for known good spare, ABS lamp goes       out every time .

2. speedo signal failure from rear drive sensor.
    No problems since.

I noticed that when I switched the ignition on, the instrument lights were just about visible. Turning the key back and on again, the lights were as they should be. I could feel the switch was a liitle rough when moving it slowly

Obviously my first port of call will be to clean / replace the ignition switch.

My question is, why did the bike power come back the first time, when I pressed the rear brake pedal  which extinguished the red warning triangular light?

Would dirty contacts in the ignition switch do this?

Have ordered a can of deoxit equilavent.

Bob

Hey Bob!

Have a look here.
Still Help!! | Ignition intermittent of, intermittent no start

Cheers

Audiobob wrote:....
My question is, why did the bike power come back the first time, when I pressed the rear brake pedal  which extinguished the red warning triangular light?
....

I think instead you should be asking "why did the red triangular warning light come ON when the bike power cut out"?

The red triangular warning light is the warning from the Bulb Monitoring Unit (BMU) for the tail light. It also comes on when you first switch the ignition on which you cancel with a depress of both brake levers. If lights remain on a bulb is blown.

You probably know all this, but the point is that what's happened is the ignition has gone off momentarily which has reset the BMU and when it comes back on straight away due to the intermittent fault, the warning light comes on just the same as if you'd turned on the ignition. This was undoubtedly caused by the failure of the ignition switch. The brake lever was not restoring power. The power was already back on before you pressed the lever.

It's a common problem. The ignition assembly needs to be removed, disassembled and cleaned. You'll probably find it in good condition because it's been packed with dielectric grease at the factory, but the grease goes hard after time.
WARNING: Small parts may cause choking hazard. Only for ages 3 years and over. 

Cleaning a BMW K bike ignition switch

Inside the ignition switch

Intermittant poor running engine

Thanks for the replies,
 
Chocolate    Holister

I will take the unit apart as per Don Eilenberger 

plus clean all related connectors 

Hopefully this will cure it.

Thanks again

Bob

audibob wrote:Thanks for the replies,
 
Chocolate    Holister

I will take the unit apart as per Don Eilenberger 

plus clean all related connectors 

Hopefully this will cure it.

Thanks again

Bob

It did for me. 

Bill

+1 on the ignition switch.  On my bike it triggered a low voltage fault in the ABS that had to be reset.  Those switches are not the best design and aren't terribly dirt/corrosion tolerant.

Hi all,

I have now done over 400 miles since I cleaned and lubricated my ignition switch and hey ho, no more problems
 All other electrical connections have now been checked for good measure, 
so happy days again 
Bob

audibob wrote:
I have now done over 400 miles since I cleaned and lubricated my ignition switch and hey ho, no more problems.

Thanks for the update!