I am a bit confused on this.

Its been eating me up for a few hours now. Its very very lte and I am unable to go out right now, to check things over, but this is my issue...

Today, I took the K100RS out for a pin and I noticed that the speedo was not showing me my speed.

Swine!

Anyway, ok, so what, its the least of my worries for now. I may need a new cable, but lets have a look!

There is no cable? Ah, ok, well where the hell is it then? I cannot even see where it USED to be?

I got a manual here and it seems to be, that the speeod is done, not through the front wheel, but through the rear!??!?

This is a good one, because my BMW K100RS... IS A TRIKE!

So, I am now wondering...

How was the speedo working before?
Was it even working before and I have only just noticed it??? No, it was working just fine, so what is up now?

I think Im going nuts?

So, lets get on to the meat of this post...

How can I get the speedo on my trike working?

The Axle is from a very old Reliant Regal, but cant I get it working from the front like a normal bike?

Simple answer from a simple person. The K speedo cable is joined under the gas tank on the right hand side, a flat 2 pronged joiner, and this is where most of the speedo problems occur (on normal K's). the speedo needle just dying sounds like this connector is loose or got some gunk in it.
The wheel end used to be attached on top of the final drive of the rear wheel, and worked by picking up an electrical pulse from the whizzing around in there, and converting it to needle movement via something that
Professor Steven Hawkins could probably explain.
However, in your case, my guess is that the end of this sensor that used to be in the final drive,(it looks like
a plastic plug end) is floating around the endosphere of your machine and has been picking up some sort of reading. Might be sitting on the driveshaft covering or something similar. 
Otherwise, call in Agents Muldor and Scully mate, because that sounds a bit weird.

You don't live near Area 51 do You?
Good luck, RT

The answer is that while you have a non K rear drive the speedo isn't going to work.
Best bet would be to get a bicycle speedo that works from the front wheel or a new after market digital speedo like most of the cafe set use when they give a K the treatment.

Do you know if it is an original K100 speedo?

heres my contribution

the normal k100 has a castellated type steel ring gear inside the rear drive with 6 poles that pass a coil mounted directly and close inside the rear drive housing . 

the cabling usually passes under the right hand side cover and connects to the loom there  as rt described earlier . and is a common corrosion point fr electrical connections .

because all the housing components are made of aluminium, only the steel castellated gear introduces magnetic type pulses into that coil )lets not consider the pinion and crown gear for the moment ).

a consideration could be, to attach six magnets to the brake drum -disc area  ( epoxy glue is used quite commonly to attach those usually ) and mount a coil quite close to them off your rear diff ....may be an original article ?

the electronics is geared up for 6 pulses per revolution

now  this all sounds easy ...there might be other issues such as the outer tyre circumference being slightly different than the standard k ...but there is a slight percentage  adjustment within the instruments  that can either boost or decline the reading at speed  a little bit .

the method for reading speed is pulses per revolution of a usually known circumference rear wheel from the sensor

hope that helps

+1 there Charlie, no good hooking up to the diff, will have to be a wheel, so the drum or disc on the back brake assembly does seem the logical option, If going to the front the stock wheel tyre combo is going to read way short and you would expect speeding tickets would be a daily occurrence.

Ok thank you for all these replies.

What has more than likely happened then, is that since you say its a magnetic pickup, much like the pushbike ones, then they must have put it onto the wheel perhaps?

I have had another look and no, I can see absolutely NOTHING that will help me out here?

Is the Speedo an MOT requirement?

The rest of the dashis all fully working ( more or less ) and yes, its a stock K100RS Dash.

The only thing that does not seem to be working is that there are 2 fuel sensor lights, an orange and a red and they dont seem to change with the orange always on and the red always off. Small issue but one that might catch me out one day.

I will put a pushbike one onto the front wheel and see how that goes... Sure, its no BMW but it might be enough to keep me legal...ish

The original BMW one should surely be adaptable to work like this surely?

Im planning on going at it today anyway... Its gorgeous outside so why not?

A gps also has a speedo in it but because its gps they cant perform a static test to confirm its working.

A speedo has been a requirement since the MoT was introduced in 1960 (I think - I don't have my usual pile of construction and use shite to hand). It gets checked during the suspension and brakes test on the rolling road. Yes, a pushbike speedo is legally acceptable. A picture of the speedo would help, because if it's not the original BMW one (I'll say it can't be) then it's possible it may be off something like a Suzuki Bandit where the speedo is driven from a sensor on the front sprocket (yes... don't ask, because I've never really studied the system). It wouldn't take much to adapt that system to something else.

Just for information speedos have been a legal requirement on all bikes registered after September 1937 in the UK.

Paul.

Ah! Memory didn't fail me. I was going to say 'since 1938' but decided that the MoT date was the relevant one for the question. Thanks for the confimation Paul.

check the connections at the back of the instruments as well. A loose/dirty connection there can cause the same symptoms. Just pull them off and put them back on might do the trick

Dai wrote:Ah! Memory didn't fail me. I was going to say 'since 1938' but decided that the MoT date was the relevant one for the question. Thanks for the confimation Paul.

Just had toadd in here, a small irrelevant mention.

You own a Guzzi 1100i?

I have a Cali 3 LAPD Classic - It was a 950, but I upped it with 39mm carbs ( instead of the 32mm stock ) and this helped its tractor-ness and it felt a better more torquier machine.
Its pipes were rotten as heck, but stainless outside so I simply gutted them out and they were straight throughs that sounded lovely and throaty without sounding silly.
Me and the ex did 130K miles on that beast touring the whole of europe over a 3 year span in a working-touring holiday.

I was going to consider the Cali 14 or 15 a while back until I saw the price... I will NEVER consider a Guzzi at the prices they are asking for them these days... Instead, I bought a GoldWing 1200.

When the Vintage first came out I was interested, right up until I took a close look at one. The instant thought was 'Harley with the engine the wrong way round'. I walked away from it.

The 1100ie is partway through a 'proper' conversion to become an '1100-T3'. 'Street sleeper' - remember those? I hated the riding position on it - too cramped and no room to move around. Amongst other things, it's meant modifying the frame to take a Convert seat. The project is on hold until I finish Brick 2 and Cali 1.

And now I've agreed to buy a 1971 ex-military Nuovo Falcone...