K75S 1988. Key goes into barrel. Turn key to "on" position and bike turns over without me pressing the green ignition switch! Happened on a really cold morning...minus 4. Re-charged battery and just tried again but the same issue. I'm assuming something is stuck on in the right hand switch gear?

Hi Boog! Boog here! Have you tried taking out the starter relay and checking that nothing has "welded" inside?
Good call......

Hang on BooG....I read somewhere that symptoms of a welded starter relay include the fact that it will turn over (even with the key removed), and do so until the battery drains down. Yours turns off when you move the key back to "off"...so there may not be a permanent contact with welding.....so gaze suspiciously at the ignition switch for a while........

Or gaze at the starter button in case its staying engaged, minus the spring.....think you are already looking over there.

The relay has permanent power so as you say that may not be the problem, but the switching of the relay will be fused and is routed via the starter button. There are posts and threads about the starter button going wrong, if you take it apart do so inside a plastic bag.....

Real cold morning, -4c, small bit of condensation inside the switch, not a problem until it freezes and becomes stuck or restricts movement. If a rise in temperature cured it temporarily maybe some WD40 or such like might be appropriate.

Yeah...that follows my current thinking. Will post again tomorrow. Thanks for your post. I enjoy talking to myself....but.......

BooG wrote:Yeah...that follows my current thinking. Will post again tomorrow. Thanks for your post. I enjoy talking to myself....but.......

Well, it is the Knuthaus. Hope you solve it.

Here is a how to dismantle.

Inge K. wrote:Here is a how to dismantle.

There are posts and threads about the starter button going wrong, if you take it apart do so inside a plastic bag.....

Before taking apart the handle bar switch, I would simply disconnect it to be sure that there is not a short somewhere in the rest of the system.
If the starter doesn't run with the switch disconnected, you have 99.99% chances to have a problem with the switch. Otherwise, you may have to follow the electrical diagram starting from the the relay coil and working toward the starter button.

Cleaned switch gear (internal). All looked fine and was cool up until the issue on Friday. Looked at relay and there was def evidence of heat! Took out the starter relay and opened it up. There was a small build up on the contact points, so I got rid of that with some wet n dry paper. I tested continuity through the relay with the contact points closed and got a reading of 0.02. Cleaned all contacts to the relay and reassembled, then re-fitted in position. Before I connected up the switch gear under the tank, I turned on the ignition with the key, but there was no joy. So, connected it all back up. Turned key in ignition but it started turning over before I was anywhere near the green switch. I turned off quick to avoid any further probs. The red kill switch does work however, and this is with the key turned to the on position. As I return the kill switch, it fires. The switch did seem fine under inspection. The plot deepens.........

Has the start button got a return spring, does it come back about 1.5mm when you take the pressure off it. Try lifting the button out a bit when you turn the ignition on and it starts turning over.  I think it was Inge Bert suggested unplugging the switch under the tank to see if that stops the starter.

Yes, it has the spring. It pulls away from the two flat metallic contacts at the rear of the switch. I will attempt to pull the green switch away the next time I attempt to turn over.

You might have to go back to check the wiring between the relay and the switch, if that's shorting to earth....?

On the starter relay is a 2 pin plug disconnect it and see if it still happens. If not then the problem is in the wiring and you will need to remove the tank and open the harness to find it, or run a new wire and isolate the old one.

Am about to undertake some elecktrickery! My research shows that the wires from the starter relay go to: Black to starter motor and load shed relay: yellow/black to fuel injec control unit and rh switch: red/brown to ignition control unit: red to battery and fusebox. Will report back shortly.

Here is the electrical situation at mo.
The initial problem does seem like a starter relay issue...cold morning...laboured starting...evidence of heating up at the contacts inside the relay. Cleaning the relay has made no difference.
When the wires on the starter relay are pulled out, only the fuel pump comes on.
I took out the starter button (green), and nothing happened at all when the key was turned. The starter button internals are clean. Both springs are present, and the brass plate is clean and in the right position.
The kill switch works.
The headlight goes off when I turn the key and get turnover without pushing the green button (load shed relay ok?)
When the kill switch is engaged, the headlight comes on when the key is turned.
Then engine does not actually fire up when turning over.
Blimey!!!!

The headlight goes off when I turn the key and get turnover without pushing the green button (load shed relay ok?)

That is reproducing the effect of pressing the starter button because it does disconnect the lights.

My instinct is check the supply wire for the starter button, possible this one is being shorted out along its route, or trapped and shorted, maybe at a cable tie, bend or plug connector. Check the earth too, there is an earth for the right hand switchgear on mine.

Even a single strand going astray can cause this sort of problem because the wires activate relays.

If the engine does not fire up when turning over then it would seem worth checking the ECU connections,

BooG wrote: The starter button internals are clean. Both springs are present, and the brass plate is clean and in the right position.

Both springs? The starter button have only one spring, the kill switch contact
plate have two springs.

Yeah....Kill switch contact plate has two....green push button, one!

Regarding the starter relay...other than checking the continuity once the contacts are closed; anything else i should be doing to check it is still ok..?~

Could there be an incorrect or incorrectly routed wire connected to the starter relay that's energising it when the ignition is switched on.....?

Well....I'm putting it away now as its 4.35pm...darkness closing in....someone has let their dog do a massive poo next to where my K is parked...my daughters home from school....I'll be on it again tomorrow!!

Put it on the centerstand, select 1st gear and turn the key.
If the starter don't turn, you have a short in the supply to the starter button.
To verify pull the clutch and the starter should be turning.

If the starter still turns when the 1st gear is selected, pull the load sh. relay.
If the starter now don't turn, you have a short between the light and starter circuit.

If the starter still turns, you have a short between the kill switch and starter Circuit.

Top man!! That will be my first task tomorrow. Many thanks to everyone thus far,for all the advice!

Just a thought, but could the contacts in the load shed relay have welded?

BooG wrote:Just a thought, but could the contacts in the load shed relay have welded?

That's what I have in mind, after reading this:

BooG wrote: When the kill switch is engaged, the headlight comes on when the key is turned.

........as you say that starter also turn over, as soon you switch on the ignition.

But if so you should also be able to put on the headlight w/o switching on the ignition.

So...a new day brings..
On stand. 1st gear engaged: Turns over.
Same thing with load shed relay removed: turns over.
So, problem between kill switch and starter circuit maybe...
However, in first gear at turnover, all the lights stay on.
If I pull the clutch lever in, I still get turnover, but with all the lights out!
Bear in mind that I am going nowhere near the green starter button yet!!
Kill switch still works when engaged.
Gear selector switch can be seen working at turnover.
As it stands (regarding the starter circuit)
1) Load shed - works when clutch engages
2) Ignition key switch - turns engine over by itself in "on" position.
3) Kill switch - Functions as I would expect.
4) Clutch switch - not functioning: engine turns over in first gear without engaging clutch lever.
5) Starter button - not functioning as i would expect, but appears to be clean and tidy inside!
6) Starter relay - engine engaging readily, but not using green button.
7) Gear digi display - appears to be working.

It looks to me that you have more than one problem/short.
One between start and kill switch circuit, the second between the kill sw.
and the light circuit.

To check the start/kill for short, disconnect the switch assy and measure
between the green wire and the black/yellow wire (at switch assy side)
this connection should be open.
If it is open, check the connection between the black/yellow wire and
every other wire at this connector.....the black/yellow wire shouldn't have
connection to any othe wire.

Do the same with the green wire and the green/blue wire to check the
kill/light circuits for short.
But with light switch on you should have connection between green/blue,
grey/blue and white/yellow.....but no other wires.

That was going well until i decided to check the ignition key switch. Removed it to the rear, the red live shorted on the top yoke, wire started smoking! I disconnected the switch coz the tank was off..but looks like the live is knackered..all the red insulation melted off. Clutch switch cable came away as well in the confusion to reveal very corroded terminals. Some soldering lies ahead...
Still busy digging a pit for myself at the moment!

If you are digging a pit you need one or more of these.

Yeah....actually the pain goes away..the world seems better....maybe people should drink a lot more! 
In the meantime, I've re-soldered and cleaned the ignition switch. No probs there. I've ordered a new clutch switch...that could be the culprit. Treading water till Friday now.

BooG wrote: I've ordered a new clutch switch...

You can use the switch for the choke warning lamp, it's identical.
A choke warning lamp you don't need anyway.

The old clutch switch cable I have cut and joined the wires together. I'll re-install this till my new cable shows up and this should eliminate the clutch switch in terms of being a possible cause.

Gonna fit new clutch switch shortly. I'm wondering if there might be anything in the starter motor that could cause the issue I'm experiencing?

No joy. I'm gonna start at the beginning and fix this sucker!
Issue: Engine turns over when key is turned to the "on" position. 
Relays (starter and load shed) seem OK. Lights off when turning over. No welding issue.
Green neutral light is on at turnover.
New clutch switch. Turnover occurs in or out of gear whether clutch lever is in or out; it makes no difference.
Kill switch works. 
Gear switch indicator shows correct gear or "0" neutral.
Engine does seem reluctant to start even though its being turned over.
Thinking time ahead....

Are you sure you cant isolate it to the right hand switch block and wiring??

Well, I've had the switchgear out and gone over it in terms of continuity. Its also cleaned and re-assembled. Everything functioning at the rh switch. At the moment I'm looking back to the starter relay. Its the type with only 1 contact. Load shed is working.

I've recently experienced the same problem but intermittant and only when the engine gets very hot and the air temp gets up in the mid to high 30's. 
The over heating is a separate issue but I've suspected the starter relay to be the cause of the instant starting problem brought on by the heat.

Have you tried swapping the relay with another?

No, not yet. I've got one coming that should arrive in a day or two. I'm gonna whip the relay out and test it with 12v to make sure it is clicking. As the engine turns over and ceases once the key is turned off, it seems to be working though. Somehow power is getting through to the switch once the key is turned on. Clutch switch is new and tested for continuity. Both relays seem to function. Earths look OK also. I'm gonna inspect the live lead to the starter relay again.
This is useful:
http://hrsbstaff.ednet.ns.ca/bvogel/K100/download/electrical/diagrams/interactive_diagrams.htm

The relay would seem to be getting power the moment the ignition is turned on. Check the incoming supply wire to the relay, if it's live the moment the ignition is on then the problem is further back. If not then it would seem to be the relay itself. A simple disconnection might show this one up.

Work back from that with the first one being the connector from the handlebar controls to the loom, just checking with ignition on and off. If opening that connector does not stop the problem then it's somewhere between the connector and the starter relay.

If that does solve the problem then it would seem to be between the loom connection and the handlebar controls. Its not easy to open up that one but it can be done.

If you trace the wire back you may find a short somewhere. There are a few potential pinch points that if the cables are crushed could become problematic. In extreme cold the insulation becomes brittle and moving a bike around in freezing temperatures using full lock is hard on the insulation.

I was in under the tank in my LT and there were what appeared to be some same coloured wires and identical connectors but that were not designed to go together. I am wondering could one of these have become an issue after changing the clutch switch..?

Also in the back of my mind is the routing from the start button to the ECU, its one of two feeds to the ECU and which should only work when the start button is pressed. I don't have the answer to this one but someone else might: if there is a fault here could it affect the starter relay? The other being the Hall sensor, this one appears to be in order.

Red/brown goes to pin 11 ICU
Black/yellow goes to the starter button... as well as pin 6 ICU

The starter can only get power thru the starter relay. You said there is no sign of welded contacts so therefore when your ignition key is turned on, the solenoid must be activating the relay contacts for the starter to turn. If the starter button is remains open then the only other place the solenoid could be getting power is from pin 6 ICU. You could be getting an erant voltage across the solenoid coming from a faulty ICU.

Just a thought but can you test for voltage across the black/yellow and red/brown wires at the relay with the relay disconnected.

This senario fits with my problem in that possibly my ICU is over heating caused by hot air coming from the radiator when the fan kicks in.
https://www.k100-forum.com/t9346-engine-overheating

I'm thinking this sounds logical. My plan is to investigate as you have suggested. As well as this, I have noticed on diagrams, that the (starter/load) relays are live with the ignition off. If the diode in the load shed is knackered, then live current could find its way up the green wire to the ignition switch; bypassing the green starter button. Gonna look at this tomorrow also, and maybe swap horn/load shed relays as I think they are the same. Its a plan of sorts, but it seems logical given the problem and its symptoms. I sound like Dr Spock..........

BooG wrote:I'm thinking this sounds logical. My plan is to investigate as you have suggested. As well as this, I have noticed on diagrams, that the (starter/load) relays are live with the ignition off. If the diode in the load shed is knackered, then live current could find its way up the green wire to the ignition switch; bypassing the green starter button. Gonna look at this tomorrow also, and maybe swap horn/load shed relays as I think they are the same. Its a plan of sorts, but it seems logical given the problem and its symptoms. I sound like Dr Spock..........

I don't think you're going to find the problem in the load shed relay diode.  On a normal bike the bike will start and run with the load shed relay removed.  Try removing it and see what happens.  It is true that the load shed and starter relay have 12 plus to them with the key off.  On the starter relay it is not to the control coil but to the normally open contact. IMHO there is nothing wrong with either of your relays.  It appears to me that your starter relay control coil is getting turned on (12+ to terminal 86 and ground to terminal 85) when you turn your key on.  Terminal 85 receives its ground through the ignition control unit and should loose its ground when the engine starts.  Terminal 86 should receive its power only when the start button is pushed.  Have you tried unplugging the right hand handlebar controls?  That would eliminate a lot of wiring to check if it stops trying to start with the key on.

kioolt wrote:I don't think you're going to find the problem in the load shed relay diode.  On a normal bike the bike will start and run with the load shed relay removed.  Try removing it and see what happens.  It is true that the load shed and starter relay have 12 plus to them with the key off.  On the starter relay it is not to the control coil but to the normally open contact. IMHO there is nothing wrong with either of your relays.  It appears to me that your starter relay control coil is getting turned on (12+ to terminal 86 and ground to terminal 85) when you turn your key on.  Terminal 85 receives its ground through the ignition control unit and should loose its ground when the engine starts.  Terminal 86 should receive its power only when the start button is pushed.  Have you tried unplugging the right hand handlebar controls?  That would eliminate a lot of wiring to check if it stops trying to start with the key on.

I agree. Starter relay appears to be working ok but (as I said above) its getting a rogue voltage to the control coil (sorry, I called it a solenoid) on the yellow/black wire at term 86. You need to focus on where that power is coming from.

Possibilities???

1. Its a short on the yell/blk wire to term 86.
*Revisit Inge's advice on post #28
*also kioolt's suggestion above

2. It's picking up a rogue voltage thru the yell/blk wire to term 86 from pin #6 ICU (I think also there is a connection to the ECU).
*I think the only option here is to swap for another ICU. Easy to try if you can find one to test the theory.

As I suggested above, a meter could tel you something like if its getting full 12v or just a trickle but enough to fire the control coil. Might give an idea about where its coming from.

Try removing the load shed relay and also disconnecting the wire on the starter.  When you do this your headlight will turn off and the starter will not run when you turn on the key.  You can either listen for the starter relay to click or my preferred method would be to put a volt meter on the starter wire that you disconnected.  It is absolutely necessary to remove the load shed relay for this to work.  If you don't you will be reading 12 volts through the load shed relay coil at the starter wire.  You will be able to take your time while checking things such as wiring harness.  Sometimes just moving or pulling on the wiring harness will cause the shorted wires in it to at least temporarily disconnect long enough for you to find the section of the harness where the problem is.  Watch the volt meter while doing this.

Kaptain Holister wrote:

2. It's picking up a rogue voltage thru the yell/blk wire to term 86 from pin #6 ICU (I think also there is a connection to the ECU).
*I think the only option here is to swap for another ICU. Easy to try if you can find one to test the theory.

As I suggested above, a meter could tel you something like if its getting full 12v or just a trickle but enough to fire the control coil. Might give an idea about where its coming from.

Yes there are two connections from terminal 86 of the starter relay coil.  One is on the Ignition Control Unit (under tank I believe) and the other is on the Fuel Injection Control Unit (under tool tray).  If you unplug both of them the starter relay should turn off.  This will not tell you a lot UNLESS you ground terminal 85 of the starter relay.  It is necessary to ground this terminal because without the ICU in the circuit the relay coil has no ground.  I'm convinced your trouble is on your plus side anyway.

Also, if after grounding terminal 85 the starter relay it turns on then you can eliminate the ICU and FICU.

I really appreciate all the help here. Thanks so much. I'm going in....happy hunting!!!

The ignition control unit looks difficult to get out, its under the tank up at the headstock but....you only have to slacken the two fixings and it slides backwards quite easily to remove it out between the frame tubes. The 'holes' are actually slots and it comes easily. Its rubber mounted, there should be a removable plastic shield protecting it.

As a safety note you will at the end of this have done a fair bit of twiddling with the fuel lines. If they are not recent it is likely they will develop splits/leaks so give a thought to replacing them but also make them a bit longer. The fuel line is cheap but its pressurised by the fuel pump so leaks are serious.

1) r/h switchgear disconnected under tank. Key turned to "on": load shed clicks, nothing else works. No click from starter relay.
2) Switchgear reconnected. Load shed relay removed: Key turned to "on". original problem again; turnover from key "on" position.
3) Load shed removed. Wires disconnected from starter relay. No voltage from terminal 86 on relay with key at "on" or "off".
12v at the connector wire (black/yellow) when disconnected from relay.
4) Load shed relay removed. Wires out at starter relay. ICU/ECU disconnected. Ground run from terminal 85 on starter relay. No click from relay. 
5) Load shed in place. r/h switchgear disconnected under tank. wires off starter. 12v at connector wire (yellow/black for terminal 86 on starter relay).

Seems like the power is finding its way to the starter relay from the black and yellow wire. Also, there does appear to be "suspicions" concerning  the starter relay. 
I think the switchgear is OK. Cup of tea and on again. My fingers are killing me....London v.cold today!!

BooG wrote:1) r/h switchgear disconnected under tank. Key turned to "on": load shed clicks, nothing else works. No click from starter relay.
2) Switchgear reconnected. Load shed relay removed: Key turned to "on". original problem again; turnover from key "on" position.
3) Load shed removed. Wires disconnected from starter relay. No voltage from terminal 86 on relay with key at "on" or "off".
12v at the connector wire (black/yellow) when disconnected from relay.
4) Load shed relay removed. Wires out at starter relay. ICU/ECU disconnected. Ground run from terminal 85 on starter relay. No click from relay. 
5) Load shed in place. r/h switchgear disconnected under tank. wires off starter. 12v at connector wire (yellow/black for terminal 86 on starter relay).

Seems like the power is finding its way to the starter relay from the black and yellow wire. Also, there does appear to be "suspicions" concerning  the starter relay. 
I think the switchgear is OK. Cup of tea and on again. My fingers are killing me....London v.cold today!!

The results of step one and two indicates wiring going to switchgear or switchgear problem. 

In step three and four I believe you misunderstood what I wanted you to disconnect.  Disconnect the big wire on the STARTER at the starter not the starter relay. Regardless of you removing the wire at the wrong place, the problem appears to be in the switchgear wiring or switchgear.  I will look at the diagram again to see if I can get a clue as to where it might be in that section of wires.

I see no suspicions concerning the starter relay at all from your description above.  No voltage on terminal 86 at starter relay no WORKEE just as it should not work.