Narrative: I'm heading over to S.F. to buy a couple of swords, get up on the freeway ramp in Oakland and notice I don't have turn signals. Quick check and find I don't have a headlight (the high beam indicator doesn't come on). Red light bulb check also isn't showing any issues but later find no brake lights either. Rather than take a chance on being stranded, I turn and run for home. As I'm heading home I monitor the electrical voltage which at 4K RPM I'm seeing 12.5 volts but not the usual 13.+.  Get the bike in the back yard and on center stand. I turn off the key and the engine continues to run. I flip the kill switch over it continues to run. I pop the side cover and remove the fuses. Something is still going on like it was dieseling. I put it in 1st gear ease out on the clutch and the rear wheel is jerkily moving. i slowly hit the rear brake and the wheel stops. I let out on the brake and the noise and wheel restart. At this point I can't tell if the engine is dieseling or if the starter motor is continuing to turn, i.e. false starting. I step on the rear brake and hold it. Engine stops. After some moments I let up on the brake and no continuation of noise or running. 

Now the fun part. I replace all the fuses in their holders. Clock has been running all this time but with fuses out it finally quit too. I turn on the key switch and the kill switch. Bike starts normally and runs. Headlight, turn signals all working. I turn off the key. Engine stops as normal. I restart the engine multiple times. Everything is apparently normal. Yech!! And BTW, I had turned off the heated hand grips before taking off the 1st time. But I try them multiple times. No issue though I don't leave them on long enough to get them hot. Now I know I've got a real demon in the electrical system. Realizing that having a real demon in there I figure the engine is just waiting to die in the most inconvenient spot and or time possible. As it is just past one I head over to the local In-N-Out burger joint and have lunch.

Now for the weird aside part. In-N-Out buggers my burger and the prettiest female mendicant I've seen in many a year hits me up for her and her brothers. I smell/rells a Demon trick and refuse to get involved. Finally get the burger right and call my buddy, Greg. He suggests it's either the load shed relay or the starter relay. So I ride home, check what I can and am looking at the circuit diagram trying to discern what might failing might give me these indications (other than the buggered burger or the mendicant). Any thoughts from the assembled masters of K75 electrics before I start swapping out parts?

Clues: issue/problem started 1) on running bike with turn signals, brake, headlight failing to energize/work 2.)Key switch and kill switch both did not stop the engine/starter (I could not tell if it was the engine dieseling  or a continuing starter that kept the engine turning over) 3.) After forced stop the engine restarts correctly 4.) electrical voltage seems to lower than normal for a running engine. (I have a small digital voltmeter that gives a continuing readout of voltage).

Suggestions appreciated.
JJefferies

edit: The turn signals and other lights were working when I started my ride. I do remember the turn signals needing to be canceled. Can't really say about the headlights though the red bad brake light signal had gone off per usual after both brakes were applied.
Model: 1990 K75C

Year and model?

With all of those things going wonky the first thing I would check, as your friend suggested, is the load shed relay.

You can swap the load shed relay with the horn relay in order to troubleshoot.

I have the different relay box layouts here:
http://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/relayboxes/relayboxes.htm

I've had something similar happen but as I pulled up, I heard the poor starter motor screaming its guts out. I back-heeled the coil cover which hit the starter motor and disconnected it. Or gave the engine enough of a thump in the right area to disconnect it. And left me with a rather painful bruise on the heel bone.

It never happened again.

Option 1:
Start button is sticking.....causes starter to stay running AND activates the load shed relay disconnecting lights etc etc just as you found. Not uncommon.

Go down this road first.
Replacement right hand switchgear may be wise, it could be button or it could be other wiring issues in it.


Option 2:
Starter relay sticking.

Dont bother trying to repair it.

It usually happens from trying to start the bike with a low battery and welds the contacts.

You will find it in the electrical box under the back of the tank [the fuses are on the side of it]. Its black, at rear of the box on right hand side, held in with 2 10mm bolts and just pulls out.

You need to find the cause, old battery and/or tired battery struggling to start will do it.

Option 3:
If your battery is 100% good you may have starter brush issue and good news is starter repair kits are cheap and a diy job. 

Option 4:
Since you had only 12v or thereabouts going home suggests you may have an issue in the alternator/charging circuit. Most common item here is the regulator on the rear of the alternator, cheap and also easy to replace, just remove the black plastic cover thats above the rear brake pedal.

92KK 84WW Olaf wrote:Option 2:
Starter relay sticking.

Dont bother trying to repair it.

Sometimes you can just whack the right rear corner of the relay box to unstick the starter relay. Doesn't always work but is free and easy to try. Depends upon how "welded" the contacts are.

92KK 84WW Olaf wrote:
Option 2:
Starter relay sticking.

Dont bother trying to repair it.

It usually happens from trying to start the bike with a low battery and welds the contacts.

You will find it in the electrical box under the back of the tank [the fuses are on the side of it]. Its black, at rear of the box on right hand side, held in with 2 10mm bolts and just pulls out.

You need to find the cause, old battery and/or tired battery struggling to start will do it.

Option 3:
If your battery is 100% good you may have starter brush issue and good news is starter repair kits are cheap and a diy job. 

Option 4:
Since you had only 12v or thereabouts going home suggests you may have an issue in the alternator/charging circuit. Most common item here is the regulator on the rear of the alternator, cheap and also easy to replace, just remove the black plastic cover thats above the rear brake pedal.

Ok, 1.)The battery was in good enough shape to restart the engine 4 times without any issue. And after your comment I put it on the trickle charger which indicated it was in good shape.
2. How do you tell if it is a starter issue if the starter is working?
3. The alternator is putting out 13+ volts. My comment was that when revving the engine the voltmeter showed the voltage slowly coming up. Whereas in the past it jumped up to full output almost immediately.

At this point I'm swapping the horn and load shed relays and replacing the starter relay (as soon as I can go and get it). Will see if that fixes this intermittent problem   Until the Demons jump back into it.
thanks and best regards
J.

Disassemble the starter; clean its commutator; replace the brushes while you're there, reassemble. Instruction is on the Tech Page at the bottom of the How-to from the forum category.

Save the hassle of rebuilding the starter.

Here's a 9K starter on Ebay. Offer $30.

That's what I'd do.

Laitch wrote:Disassemble the starter; clean its commutator; replace the brushes while you're there, reassemble. Instruction is on the Tech Page at the bottom of the How-to from the forum category.

Yeah, but I did that when I assembled this machine less than 20K miles ago. I'm loath to go about replacing parts unless I can cite a specific failure. So far the starter hasn't failed. If anything it's been working too well. I'll try the relays first and then see if there is any repeat. Just wish there were a technically reasonable way to go about diagnosis instead of just shotgun replacing parts. If I replace the relays and it occurs again then it would seem to me to make sense to pull down the starter and go through it. Of course I could get stranded again. But if I've not replaced the right things then it is possible to have that happen.

OBTW, met a fellow last week who'd just bought his first K75, a 1991 model with 9K miles on it and in pristine shape. Paid $5K for it.  Very pretty machine in the BMW red (more orange than red I thought).

The good thing about trying the load shed relay first is that you can just swap with the horn relay so it's free.

jjefferies wrote:

Laitch wrote:Disassemble the starter; clean its commutator; replace the brushes while you're there, reassemble. Instruction is on the Tech Page at the bottom of the How-to from the forum category.

Yeah, but I did that when I assembled this machine less than 20K miles ago. I'm loath to go about replacing parts unless I can cite a specific failure. So far the starter hasn't failed.

Don't give it another thought then.

It sounds to me like there is a problem with the wire that feeds the signal from the "Start" button to the starter relay.  That is the first place I would look.

The other posters are correct about the load shed relay shutting off the headlight and turn signal functions.  The thing is, that is exactly what the load shed relay should be doing when the starter is running, so in my mind, it is doing what it's supposed to do.

Start at the "Start" button.  Pull the switch gear off the handlebar and look at the back of the switch to make sure everything is correct.  from there, follow the wiring back to the start relay paying special attention to the big connector for the right switch under the tank and the wiring in the relay box. 

You are looking for a way that +12v can get into that wire.

Another clue is that the starter operation should be inhibited when engine speed is above 700rpm.  This didn't seem to have been happening as you were riding the bike.

If I recall correctly, it is the ignition control unit under the tank that performs this function, but I don't know exactly how it is done.  There is a ground wire from the start relay that goes to the ICU.  It might be that ground is how the relay is inhibited.

This sounds like the classic case of the starter relay stuck on due to low voltage while cranking. Typically caused by a low battery, but if the battery is good, look elsewhere.

I think the low voltage while riding could be due to the starter continuously turning, but we want to find out about low voltage while cranking. 

I think you're saying the heated grips were on before starting, then you turned them off before riding. You  tried to repeat the problem multiple times without luck, but I'll guess that was with the heated grips off (while cranking, not running) If the problem can be repeated with them on while cranking, you might have a short or unwanted resistance in that part of the circuit.

Point-Seven-five wrote:If I recall correctly, it is the ignition control unit under the tank that performs this function, but I don't know exactly how it is done.  There is a ground wire from the start relay that goes to the ICU.  It might be that ground is how the relay is inhibited.

The Brown/Red wire from the start relay coil to the ICU is a switched ground. It is switched to normal ground through a transistor inside the ICU. The ICU knows the engine rotation speed through the hall sensors. When power is applied to the Kbike and the engine RPMs are below 700, the ICU switches the transistor on and current from the start relay coil can flow to ground. When RPMs get above 700, the ICU switches the transistor off and now there is no circuit to ground for the start relay. Thus the starter is inhibited when the engine is running.

robmack wrote:

Point-Seven-five wrote:If I recall correctly, it is the ignition control unit under the tank that performs this function, but I don't know exactly how it is done.  There is a ground wire from the start relay that goes to the ICU.  It might be that ground is how the relay is inhibited.

The Brown/Red wire from the start relay coil to the ICU is a switched ground.  It is switched to normal ground through a transistor inside the ICU.  The ICU knows the engine rotation speed through the hall sensors.  When power is applied to the Kbike and the engine RPMs are below 700, the ICU switches the transistor on and current from the start relay coil can flow to ground.  When RPMs get above 700, the ICU switches the transistor off and now there is no circuit to ground for the start relay. Thus the starter is inhibited when the engine is running.

Interesting. So, in this case, if the ICU has gone wonky and the starter relay is still grounded above 700 RPM AND the start button/wire is shorted then the starter could be running while riding which could be the cause of the voltage being 13ish instead of 14ish where it should be. And the load shed would be kicked in by being start mode which would cause the headlight and other load shed circuits to be open.

Just guessing,

That's kinda what I was thinking.

duck wrote:

robmack wrote:

Point-Seven-five wrote:If I recall correctly, it is the ignition control unit under the tank that performs this function, but I don't know exactly how it is done.  There is a ground wire from the start relay that goes to the ICU.  It might be that ground is how the relay is inhibited.

The Brown/Red wire from the start relay coil to the ICU is a switched ground.  It is switched to normal ground through a transistor inside the ICU.  The ICU knows the engine rotation speed through the hall sensors.  When power is applied to the Kbike and the engine RPMs are below 700, the ICU switches the transistor on and current from the start relay coil can flow to ground.  When RPMs get above 700, the ICU switches the transistor off and now there is no circuit to ground for the start relay. Thus the starter is inhibited when the engine is running.

Interesting. So, in this case, if the ICU has gone wonky and the starter relay is still grounded above 700 RPM AND the start button/wire is shorted then the starter could be running while riding which could be the cause of the voltage being 13ish instead of 14ish where it should be. And the load shed would be kicked in by being start mode which would cause the headlight and other load shed circuits to be open.

Just guessing,

So could this be an intermittent sort of thing? As at last check all systems were working properly. Chasing down intermittent issues can be so frustrating until they aren't intermittent and then you are usually stranded by the side of the road.

If the starter keeps running when you turn the key off then that means the starter relay is stuck because it should only send power to the starter motor when it gets energized by 12V from the start button via a BLK/YEL wire. When you turn the key off there is no power to the start button.

How the starter relay got engaged while you were riding might just be a fluke or perhaps the starter relay has gone bad somehow. If this ever happens again where the starter motor keeps going then I would try whacking the right rear corner of the relay box to see if that unsticks the relay. Otherwise disconnect the ground cable down near the shift lever to disconnect the battery.

If you want to make disconnecting the ground quick and easy "just in case" then you can attach the battery ground cable to the transmission with a M6x50 knob with two "locked" nuts at the end. I did this on a K75 that came to me with starter relay issues. Thankfully I've never had to use it but it's there if I need it. 

If all of the above stuff checks out, I'm liking the idea from Laitch that the problem is in the starter motor, cause that is directly in the circuit that could drag the volts down from the battery to the starter. You replaced the brushes 20,000 miles ago, that's good, but the commutator might have been dirty. Since the starter was spinning for so long, that might have cleaned it up so that you can't now repeat the problem.

Like duck did, I installed a battery isolator switch between the battery earth strap and the gearbox, it's good for peace of mind that you can stop it quickly without putting a high load on the circuit as with a stall. It's about $10 and 10 minutes. After I did it I said to myself, daveson that was so easy, why did you leave it on the to-do list for so long.

daveyson wrote:If all of the above stuff checks out, I'm liking the idea from Laitch that the problem is in the starter motor, cause that is directly in the circuit that could drag the volts down from the battery to the starter. You replaced the brushes 20,000 miles ago, that's good, but the commutator might have been dirty. Since the starter was spinning for so long, that might have cleaned it up so that you can't now repeat the problem.

But the starter can't get power to spin unless the starter relay is engaged.

Except for when the relay is stuck.

daveyson wrote:Except for when it's stuck.

That's what I meant by engaged, as in having a closed circuit from 30 to 87.

Yep, agree. So everything was working normally, but the low voltage between 30 and 87 caused it to stick. 

So when the volts went low, the amps went high, and the contacts got hot and sticky, is my guess.

It would be good to clean the load shed relay contacts, it might have turned on later than usual because of this. You don't need it to start the bike, it just reduces the load while cranking. Anyway who wants blinkers on while cranking, who wants to press the horn button while cranking. Maybe to wake up if you have a caffeine deficiency, but coffee fixes that. In OZ the headlight is optional during daytime, so it's not much help for my brick. When I do the headlight relay, I'll use it. It's on the to-do list. 

The only reason I used this type of battery isolator switch is it was the only type at the local hardware store.

I'll give you my experiences on this issue and electrical gremlins...

1) Check the Backbone Ground and all  its wires to the ICU, FCU as well as any ground from the various relays feeding to that at their point of contacts.
  I didn't make the 2021 Montana Rallye because of intermittent shutdowns (thought it was bad gas) right at the Mid-Point from Klamath Falls and Bend    Oregon..  AAA Premium got me out of that, then rented a UHaul to shuttle the beast back to Bay Area CA from Bend. 

2) I sent in the ICU and FCU which CAMO had recertified no issue .   Shot-Gunning parts did not resolve the issue...  I found the bad ground from the FCU Ground with the Ohmmeter hooked up and moving wires....   It was the last thing I checked in the excellent T/S document sequence in Bertrand Vogel (Crazy frog)'s piece....  FCU Pin 13 to Ground!  Cleaned the ground also grounded the frame to engine as well in several areas burnishing all points and when tightened protected them with Clear Nail Polish!

The Backbone Grounds I soldered the terminal ends (Factory had just crimped them).  Also used a star lock washer for the ground bolt.

https://bmwmotorcycletech.info/K100%20troubleshooting%20Starting.pdf

Also I would look in the (Lunch Bucket) Relay box very carefully wire condition at the fuse block and any wiring leading to the relay connector basses as well as the receptacles conditions for burning from hi resistance.

If nothing is amiss on this.... and have the Tank Off (Major PITA for a RT anyway) I recommend to change out all the above with New Items what has been recommended by the posts previous...  Breaking down on the freeway with all the fools looking at their devices is not a good place to be...

Left Turn Signal switch ASSY, Ignition Switch, Load Shed Relay, Starter, Dual Contact Starter Relay all at a reasonable price from EME.

Lately I had an issue where the telltale Batt light was glowing and the volt meter was wavering after riding a while thought the diode installed years ago for this was failing....  I was down South of San Jose, refueled and the bike wouldn't start...   Was not getting ANY noise from the Fuel pump nor relay activations.  Was just going to call AAA when it started, I then drove home...

I Pulled the Tank off (Love that Job)  And proceeded to change the starter and start relay (dual contact upgrade).  I also went to the famous ground...  and that was good.

While looking in the Lunch Box - noticed that the wire that is duel crimped to the input from the ignition/kill switch circuit to Fuse 1 the leg going the the F1 Relay at the crimp (very hard to see) was hanging on insulation where the conductor was just barely touching....

Repaired that (which was the problem evidently).  Put all the items together and bike is now running 14 Volts steady at the indicator... (installed the 50 Amp unit from Duck a few years ago).

Moral of the story, is to methodically check out all the connections/ground etc.  That's how I solved the 2021 issue, but maybe this was causing it as well?  Sorry for the long winded speech but I find with this machine, nobody out there will touch it because of the complexity of troubleshooting intermittent issues  and if they are out there they are cost prohibitive so this is an owner thing most likely.

I had the stuck starter relay problem once, I accidentally dropped it on the ground from about one foot height, that fixed it, and the problem never returned.

OK let's say you've cleaned everything up and installed a battery isolator switch for peace of mind, I'll guess that the problem won't return. This thread reminds me to once again do the occasional backspin tip from Johnny.

And let's say one day the relay gets stuck again. A short sharp tap will probably fix it. The terminal on the starter motor should be earth at all times except for while the start button is pressed. Using an old fashioned test light with the clip on battery positive and the probe on the starter terminal, the light should glow. If it doesn't glow, you have just isolated your problem to a poor earth at the starter motor.