Not quite sure what is going on with my 1984 K100 - I noticed a while ago that main beam would not function from handlebar headlight switch but dip was still working normally and I generally have dipped beam on all the time.  Main beam would work if I pressed the headlight flasher switch but obviously not practical to ride holding that switch.  As I normally ride with dipped beam on all the time I haven't really bothered too much about it until now because I mostly use this bike for daytime only motorcycle instruction etc.  It was pointed out to me on the last training session that I didn't have my lights on! It seems that I have lost low beam too now! Today I decided to investigate further.  My first thought was to try a new headlight bulb, a bit of a faff to replace the bulb and still no dipped beam or main beam but main beam flasher still works.  I suspect that the main beam issue stems from the right hand switchgear for which I do have a replacement in the pipeline, as mentioned in another post. Unfortunately, I now have no low beam either ! Just the little sidelight.  Anyboby got any guidance as to what I should do next ? Thanks in anticipation of your feedback etc.

Do you have ground (or earth) working on the socket?
This is a common wire for both low and high beam.

I guess suspect the right hand switch assembly

but before you go too much further, clean - test the under tank connections  from the right hand switch ...and the left hand switch wiring connector  
from memory the flash gets its power from another feed besides the main power from the right hand switch ...or is wired differently in any case

corrosion in these connectors is very common ..if not inspected - serviced regularly

of corse it may be in the switch itself ...also a common issue  and one which has helped many of us decide to install lighting relays ..to reduce the current through the whole light switching paths

hope that helps some

I already have an Easter Beaver relay kit waiting to be fitted but am reluctant to fit that until I can get the original gear working as intended.  Thanks for all the replies so far - this forum really is wonderful

Crud in the lefthand switch assembly. As Charlie says, the flash power is on a different feed from the righthand assembly across to the left. Power feed to the headlight dip/high is the yellow/white wire. I'm willing to take a large bet that the problem is the high beam contact in the leftside switch is crudded over.


... okay, I admit to having fixed two with exactly the problem you describe and that was the solution. I'll take another bet that Murphy is waiting over there in the shadows to trip me up

Crazy Frog wrote:Do you have ground (or earth) working on the socket?
This is a common wire for both low and high beam.

Thanks for the reply CF - how would I test this with my multimeter - I am hopeless with vehicle electrics ?

Dai wrote:Crud in the lefthand switch assembly. As Charlie says, the flash power is on a different feed from the righthand assembly across to the left. Power feed to the headlight dip/high is the yellow/white wire. I'm willing to take a large bet that the problem is the high beam contact in the leftside switch is crudded over.


... okay, I admit to having fixed two with exactly the problem you describe and that was the solution. I'll take another bet that Murphy is waiting over there in the shadows to trip me up

Thanks for the prompt response Dai - I will attempt to clean/make good that switch as time permits. I think it is time that all my electricals were treated with DeOxit again - it has been 2 years since they were last done.