As it is very difficult for most people to follow the full electrical schematic, I made this simpler one about the starter relay and load shed relay.
The function of the load shed relay is to disable lights and accessories to give the maximum power from the battery to the starter.
This may help you to understand how it works as well as troubleshooting a starter not turning.

The way that the load shed relay works is confusing but in fact cleaver.
The relay coil is fed with the positive(+) from the ignition switch on one side and from the ground(-) coming from the starter on the other side(the ground is passing through the inductor of the starter motor). when you push on the starter button, this ground will be switched to positive and the load shed relay coil will then be fed by a positive(+) on both sides (This is like not having power). At this point, the load shed relay will be released and the lights and accessories will go off.

Note: if the gear box is in neutral, the starter button is fed from the digital gear display(power passing through a diode). If not, it is fed by the clutch switch.

THIS IS WHY PEOPLE ARE TALKING ABOUT THE GROUND COMING FROM THE STARTER. If you have a bad starter, your lights, flasher,horn and fan may not be working as the load shed relay coil doesnt get its negative.

Note: When the battery is low, DO NOT TRY TO START THE BIKE. You may end up burning the starter relay (a $130 mistake)

Thank for this. So I understand a little more about troubleshooting these relays....will the starter attempt to fire the bike, if the relay is faulty? Or not engage at all?

If the load shed relay is faulty, will the bike turn the starter, but not fire the bike?

Thoughts on testing the integrity of them? will using a test light and the battery work or damage it?

Thanks for posting the diagram, Bert.  Now I finally understand what is going on with the load shed relay.  Didn't realize that it is energized closed to power the circuits it controls and goes normally open when the starter is energized.

One question, though.  Is there supposed to be a ground drawn on the other side of the starter relay coil?

Point Seven Five,

No, the other side of the starter relay coil does not go to ground directly. Bert has exercised artistic license in his drawing and eliminated huge sections of the bike's electrical system for simplicity's sake, including the ICU and ECU. The other side of the coil goes to the ICU. Below 700RPM, the starter coil gets its ground connection through the ICU. Above 700, the ICU prevents the starter relay from engaging for safety.

Cool, info burned to whatever memory I have left.  Still, it would be handy to show the ECU contact with a note about the 700rpm logic.

Point-Seven-five wrote:Cool, info burned to whatever memory I have left.  Still, it would be handy to show the ECU contact with a note about the 700rpm logic.

Due to average age of K riders certain aspects are committed to memory to force us to remember.......that 700rpm or 710rpm is important.....

"Due to average age of K riders certain aspects are committed to memory to force us to remember.......that 700rpm or 710rpm is important....."

To be precise 711rpm.....no I don't know and I doubt BMW knows either.

Thanks k100LT

I have symptoms that seem to indicate a issue with the load shed relay - as well as symptoms that are NOT consistent with a bad load shed relay.

Recent history: the bike ran fine and as part of maintenance I replaced the voltage rectifier since the brushes were out of spec. I installed the new voltage rectifier and the bike starts fine and the voltage across the battery terminals indicate the bike is charging (13.8v).

Problem: in completing this work I have lost lights, turn indicators, horn, hazard lights, and temperature gauge - classic load shed relay activity. BUT, these items do NOT work before the bike is started. Normally, when the ignition is turned to the ON position, these accessories work until the starter button is pressed at which time the load shed relay shunts the power to these items. The bike runs fine. In summary, the lights, turn indicators horn, hazard lights, and temperature gauge should work with the ignition ON and prior to the starter button pressed - but they don’t. 

The fuses are good.

I am perplexed inasmuch as everything worked fine until I removed the ECU, battery and voltage rectifier. Note, I did not remove the alternator to complete this work.

What am I missing?

Dave

Try swapping the load shed relay with the horn relay.


Your symptoms are consistent with a permanently open load shed relay. When you turn the key on,  you should hear a click from the load shed relay.

davemadsen wrote:What am I missing?

You're missing the opportunity to smack the load shed relay with a screwdriver handle, unless you didn't want to admit trying that.

Problem resolved. I whacked (technical term) the load shed relay with no satisfaction so I whacked the horn relay and the lights came back on - Eureka! 

Is this a one-off incident do I need to plan on replacing the relay? Also, I noticed the load shed relay has a fifth pin. So while it was recommended to swap the horn relay (4-pin) with the load shed relay (5-pin), are they in fact interchangeable?

The pins and sockets of all relays appear corrosion free and still coated with the dielectric grease I applied during previous maintenance sessions.

The five pin relay is the fuel relay. There are quite a few drawings which label the relays wrong. 

Top left is fuel relay, top middle is load shed relay, top right is horn relay. You can think of the horn relay as a spare for the load shed relay, but then horn won't work if it's failed.

Ahhh, the Clymer’s manual has the relays mislabeled. I see now I had whacked the load shed relay.

Thanks you so much for following up and providing the clarification.

No worries. Another quick way to verify it, for example, remove the top right relay (horn relay) then the horn won't work. Remove the fuel relay, then the fuel pump won't work, etc.

davemadsen wrote:Is this a one-off incident do I need to plan on replacing the relay?

You'll probably be motivated to replace it after the second or third time you've smacked it.

BEFORE YOU GO OUT AND BUY NEW RELAYS: the ones on the K-series are DIN-A standard which means they have the switched power (pin 30) and coil power (pin 86) swapped over compared to the later (and off-the-shelf) DIN-B series. Secondly, despite having five pins, the five-pin relays are not changeover relays. See this:

https://www.k100-forum.com/t15966-relays-relays-relays-types-and-substitution