I took Dietzie out for a few loops around the block and this light is on.

What does it mean?

Emergency flashers

I found the bike manual. It is a rear brake light monitor.

The funny thing is both the tail light and brake light are working.  hmmm....

Are both brake switches lighting the brake light?  That light will stay on unless both front and rear brake switches are closed to light the brake light.  The function tests both the bulbs and the switches that turn them on.  My money is on the rear brake switch being bad.  It's in a nasty place.

@Point-Seven-five wrote:Are both brake switches lighting the brake light?  That light will stay on unless both front and rear brake switches are closed to light the brake light.  The function tests both the bulbs and the switches that turn them on.  My money is on the rear brake switch being bad.  It's in a nasty place.

Perfect! Thanks.

Both brakes work fine but when I pumped the rear brake pedal a couple of times the light went off. The rear switch must have been sticky.

This bike only has 27,655 km's on it. My plan is to flush all fluids and replace the fuel filter. She also needs new tires from age. Her last service was in 1999 at 20,xxx km's other than oil changes. In spite of that the fluids look surprisingly good.

The clutch was nice and light and the tranny clicks snickety up and down the gears.

That's great!  Let's hope that is the most serious issue your bike has, although with the long storage, I would expect that it may have some problems with the fuel system being varnished, particularly the injectors.  It's never too soon to get a good dose of fuel system cleaner in the tank with some fresh fuel.  That is assuming that ethanol hasn't turned the fuel pump mount to black goo and spread it around the fuel tank.

Well done getting your K!  My bulb monitor is completely intermittent and has been since I picked up the bike a year and a half ago.  The bulbs are fine and I have replaced the rear brake light switch and have checked the front switch more than once.  I believe that some folks have disabled this feature and I am thinking of doing the same since I have never been able to correct it.

@Woodie wrote:My bulb monitor is completely intermittent and has been since I picked up the bike a year and a half ago. 

Describe how the monitor is intermittent, Woodie.

It will work properly for awhile and then it just won't shut off.  Occasionally it will turn off during a ride when I'm on the brakes.  I can definitely see the light flicker/pulse (and not turn off) when I operate the brakes after I've started the bike.  An intermittent short of some kind in the BMU maybe?

Although these K100's are way too new for me my hunch is you still have a switch problem.

One of the nice things about my 84 V65 is that its rear brake monitor light is only on the bulb and the switches work only on the brake light.

If the bulb contacts are poor this light will flicker...........take out rear light and rear brake bulb and clean them well.

I will definitely do those things again but I have cleaned contacts a couple of times, replaced the rear brake switch and thoroughly cleaned (pumped it full of deoxit and worked the plunger) and tested the front brake switch which was not indicating any fault. At the end of the day I have become accustomed to having that bloody red light on a lot.  Lately I've been thinking I might just pop the bulb out of the instrument cluster.  It's definitely not the most important safety feature to me since I check the brake lights the old fashioned way fairly regularly.

@Woodie wrote:It's definitely not the most important safety feature to me since I check the brake lights the old fashioned way fairly regularly.

What sold me on this unit is when the triangle lit in traffic. I pulled over and discovered my taillight was burned out. I replaced it with a spare and rode off.

If you haven't yet, pull the monitor from its socket then clean its terminals and sockets. If you decide to disconnect it, there's this .

as olaf says

the near only reason that the indicator comes on during a ride ...after getting going and extinguished ...is that the rear globe holder  or wiring to the globe holders ...could be faulty , or a faulty fuse   don't forget some of the electronics has dual supply .
  

I have seen this exact same thing a couple of times

the first time was due to the socket of the running lamp had become corroded ...a good clean up of both lamp holders  fixed that issue ….but again it happened ...this time due to a flakey globe about to die ...it would come on almost every time but I notices some slight brilliance differentiation ….the globe was turning black inside the glass envelope ...and the filament was jumping about inside the globe ...bright one minute, dull the next …

the circuit actually measures the current going through it to the appropriate globe ...and if it falls low in current draw ...bing the warning lamp is back on …

replace both globes with something of a good brand name ...could be a helpful thing to do
also feel the cable going to the rear lamps ..along its length from the loom to the ducktail , feeling for any distortion especially near the top shock mount

we have seen pinched cables  under that shock mount before ...sometimes causing a short ...sometimes causing a voltage drop because of fractured cables ...meaning that the current draw of the globe cant get to the right level to keep the warning lamp off . at every operation .

good luck with the solve

The front brake switch is the same as the clutch lever switch (and some but not all rear brake switches). You could try swapping front brake and clutch switches. The lack of ability to dismantle them means that attempts to clean by injecting stuff as not overly reliable. I had exactly the same issue with BOB the Blue Old Bike, and it wasn’t sorted until the switch was replaced. 

As Laitch said, it’s main purpose is to detect a blown bulb, but as they get older, poor connections as Olaf said, and failing switches give the same no-brake-light result so it is a useful thing to keep in place. 

Bill

Okay so some early morning diagnostics has revealed the front brake switch to be the culprit.  I ordered a new one last fall to replace it but when I went to do the job I couldn't get it to fail.  I'll pull the tank tomorrow morning, do the swap, and report back.  And yes, this morning it didn't work, then it did, then it didn't  

@Woodie wrote:And yes, this morning it didn't work, then it did, then it didn't  

I thought that was when you were checking the indicators.  

Bill

Mission complete - new switch is in and all systems are go.  Pprince, thanks for allowing me to hijack your thread.  Twice in the past when I was looking at the front switch I couldn't get it to fail.  

Of all the parts that I want to replace or improve I think fuel line disconnects are now up at the top of the list to install.   Repetition is the mother of all learning and I can get the fairings and tank off quite efficiently now but these would make the job infinitely faster and easier.

Thank you all for encouraging me to deal with this and get it sorted!

So I had this thing working repeatedly this morning.  Tank and fairings back on - no longer working.  Repeated and sustained swearing didn't fix it.  I'm thinking now that the problem lies somewhere in the wires between the connection and where that circuit ties into the BMU.  Oyy...