Lately I've suspected that one or more ground may be corroded somewhere in one of the nooks or maybe crannies of my bike. I have used deoxit as many here have recommended and cleaned as many of the obvious connections I could with steel wool, wire brushes, deoxit, files, and sandpaper. Please tell me which grounds I may have missed. I have "treated" and made sure were properly grounded all of the following ground wires: the obvious cluster of brown wires under the gas tank, the one to the engine directly from the negative battery terminal, one to a bolt behind the footpeg mounting bracket, one on the starter (or maybe it's the alternator, I can't remember). If anyone could post a complete list of all grounds that are to the frame or to some component which eventually goes to the frame that would be even better than telling me the ones I missed. Also a BMW mechanic told me via email that a bolt toward the right rear side of the frame, a bolt which holds the engine to the frame has a ground and looks like this:


Can anyone clarify what he's talking about? I can't seem to find a wire leading to that spot on my bike...

I have never seen an earth wire on that bolt. There is one more I can think of and that is below and just behind the fuel rail between #3 & #4 injector, it is not very apparent and gives the fuel injection computer an extra earth. There may also be a earth wire that goes from the cluster under the tank to the right master cylinder and it is very neccessary to your well being and can prevent a throttle lock up. Other than them and what you mension I can't think of any others.
Neither the starter or alternator has earth wires you may have mistaken the 6mm black wire with a smaller one next to it on the starter which supplies power when the start button is pushed.

FreebasserSF wrote: Also a BMW mechanic told me via email that a bolt toward the right rear side of the frame, a bolt which holds the engine to the frame has a ground and looks like this:
Can anyone clarify what he's talking about? I can't seem to find a wire leading to that spot on my bike...

It`s the mounting lug itself which is the main ground connection between the engine and frame.

Inge K.

Ah Yes thanks Inge I hadn't thought about that earth, the other 2 points on the engine are rubber mounts on the K100 but the gear box also has good earth points.
I see your winter has not driven you crazy yet or do you spend the winter in Spain and not tell us.

K Freak wrote:I see your winter has not driven you crazy yet or do you spend the winter in Spain and not tell us.

Not yet........but -8 degree celsius and snowing.......keeps you inside, throwing pieces of wood into a
big iron box.

Spain would be a great idea, my fellows at work and I have often speak about putting the factory on a
raft and pull it direction south............the stock holders doesn`t agree.

Inge K.

Aha! So the bolt should be taken out ran, over with some lube and a dye to be sure it's clean, and then re-inserted to confirm ground.

K Freak wrote:Ah Yes thanks Inge I hadn't thought about that earth, the other 2 points on the engine are rubber mounts on the K100 but the gear box also has good earth points.

What do you mean about the rubber mounts on the engine? Also where are the grounds on the gear box?

The two front mountings on the frame, is rubber mounted.
The two rear mountings (at gearbox) is direct mounted (which also give electrical connection).

Inge K.

FreebasserSF wrote:Aha! So the bolt should be taken out ran, over with some lube and a dye to be sure it's clean, and then re-inserted to confirm ground.

Watch out when you removing this bolt, as it should be a shims (if needed) between the frame mounting lug and the bellhousing.

Inge K.

Great tip Inge thanks for that I am just about to treat that bolt.
Regards,
K-BIKE

"There may also be a earth wire that goes from the cluster under the tank
to the right master cylinder and it is very neccessary to your well
being and can prevent a throttle lock up."
Sorry, but I don't understand this. What is the right master cylinder? The front brake pump? A throttle lock up? Does this mean the throttle will not close?

brickrider wrote:Sorry, but I don't understand this. What is the right master cylinder? The front brake pump? A throttle lock up? Does this mean the throttle will not close?

Yes, it`s the front brake pump...........and worst case scenario is that your throttle won`t close.
(but if the specific problem should happen, you probably just end up with a throttle that is stiff to operate).

Early in the life of the K it was some issues with front brake switches that shorted, and the only way
the current could find ground, was through the throttle cable.
So since then (05/84) the K`s got an additional ground wire on RH lever assy.

Inge K.

brickrider wrote:"There may also be a earth wire that goes from the cluster under the tank
to the right master cylinder and it is very neccessary to your well
being and can prevent a throttle lock up."
Sorry, but I don't understand this. What is the right master cylinder? The front brake pump? A throttle lock up? Does this mean the throttle will not close?

BMW found that under some fault conditions that the extra current was earthing via the throttle cable which was gettinh hot and melting the inner liner and binding the cable so that it didnt return properly. I was going to type right switches and changed my mind and put master cylinder (front brake) but didn't delete the right bit sorry for the confusion.

My K100RS is a 1985 model, so this could well be something I need to pay attention to. When I first acquired the bike I did some work on the front brakes, but I don't recall finding any earth wire on the brake master cylinder. Where would I find the connection point, if the wire is indeed there? TIA

It is a black wire, not brown as are most earths, and connects to a 4mm allen head bolt to the front inner lower corner of the master cylinder assembly.

It should be mounted on all models since 05/84.



Inge K.

Also on mine there is a large flat braided earth strap that connects to the lower fork clamp and goes back to the earth point on the main frame under the tank.

When i had everthing off for the headlight relay stuff, i noticed that the lug on the end of it that attached to the fork clamp had snapped off. Probably from fatigue,but definitely worth checking. I don't know if all the models have them though.

Inge, you wouldn't happen to have a photo of that ground?  I have a 4/85 RS converting to RT.  Been in the shop for a couple of months, brain is not remembering where that wire goes?  Black wire with loop on end.

Inge K wrote: Early in the life of the K it was some issues with front brake switches that shorted, and the only way
the current could find ground, was through the throttle cable.
So since then (05/84) the K`s got an additional ground wire on RH lever assy.

My RT is 08/84, doesn't have this, but the LT does have it........Good post.

Unless I am wrong and this isn't part number 25, but I think it is

Yep thats it. I have also seen them attached to the other bolt that holds the master cyl at the front

Other end to the central ground under the tank.

I did find that ground I attached it to the front mount on master cly.  That is where it is on my 89 RS.  I would think either location grounds the  throttle?  Right?

Yep that's it

I just checked my K1100 front brake master cylinder (20mm Brembo) and there is no apparent connection for the ground.  Is it required on the K1100 front brake master cylinder or is that ground wire ONLY required for the K100 MC?

16V's got a different kind of front brake lamp switch.

So Inge, I take it this means the ground wire is not required on the K1100 front MC. The short circuit cannot happen because of the different right-hand light switch assembly's design and therefore current will never try to find its way back along the throttle cable.

Yes, you're correct Robert....16V switches has a plastic housing...
much less posibillity to short to ground.

8V switches has partly a metal housing.