My K100 has been acting up. Indicators and horn not working sometimes (both riding and engine off), also not starting (but getting a click on starter press), and the headlight not coming on before start.
The weird part is, if I put it in gear and rock the bike back or forward, the headlight will come on and then it will start.
I have had the battery checked at a battery shop, and cleaned the terminals and earth on engine block.
I'm running LED indicators with resistors, and aftermarket speedo, and lights at both ends.

Mine was doing silly things like that and it was the starter motor causing all the electrical gremlins

yep  agree waz

get the kit ...brush and backing plate (including the earth side brush ) from all the usual places

and do the starter

some fine grit wet and dry can help cleanup the armature .....don't forget to clean off the swarf of copper with some cleaner ...perhaps electrolube ..electrical cleaner ...perhaps even carbi cleaner at a push will get all the garbage out of the wrong places

good luck !

Thanks guys, I new this forum would the fount of all knowledge!

Go gently on cleaning the armature, if its left rough it wears out the brushes....Lidl near you? Some of their W5 cream cleaner is as rough as you need.

This Info "How to" clean the starter could help.
If this is this is the issue.

https://www.k100-forum.com/t2342-starter-motor-cleaning-tutorial

Cheers

Thanks for the info, and Robmack for the tutorial. All working great now. God knows how long an auto elec would have taken to find the problem!

nice result

I'll hijack this thread as the issue seems resolved, congratulations.

My bike 1990 K75 is giving me some trouble at the moment.

Was on the way to work today, pulled the clutch in preparing to stop at a traffic light. it was a cold morning and the bike not yet warmed up, so the engine died. Usually it starts up again without trouble, but today the dashboard was dead. If I turn the ignition of, the little clock comes on again. but if I turn the key to ON, the clock dies, no lights on the dashboard or headlights and does not start.

Same happened to me a few days ago, parked the bike, went shopping and when I came back 5 minutes later it was dead.

Both times, after 15 minutes without me doing anything other than aimlessly wiggling a few cables, checking the fuses and angrily looking at the bike it starts as if nothing ever happened.

Any ideas on where this mysterious behavious may come from?

The fuses may be the problem best at the age of these old stuff is to replace the fuses with new. They dont blow but will fracture where you cant see.
The ignition switch is one of the things to check, with some care you can get them apart and clean then which often solves the problem.
In general loose and coroded connections, use DeoXit it's a good cleaning agent but is a bit expensive but worth it.

Hi Thank you for your reply. The fuses are all new or max 6 month old and look fine.  but will check again. will have a look at the ignition switch again.

Sounds exactly like the problem I had last year with my K75RT.  I cleaned what looked like a perfectly clean ignition switch and haven't had a problem since.

For some reason, the designers decided to build an ignition switch that had a very light pressure and marginal travel on the contacts.  It doesn't take much to prevent the switch from working.  Do a search on K bike ignition switch for several nice photographic tutorials on taking the darn thing apart and getting it clean.  One of them is in German, but the photos are very good.

Perfect, that looks doable and gives me a place to start

not so perfect, I'm stranded at the office, bike would not start after work and I had to abandon her for the momen, all the angry staring and incessant wiggeling did not have the desired effect, will try again tomorrow