Hello all!

New to the forum and K bikes (and any bikes for that matter)

A friend and I have started an ambitious project of taking a bucket of parts of a K100RS and bringing it back to life.  We've made good progress in the build so far however we are currently trying to work through the wiring loom (which wasn't on the bare frame or labelled when purchased).  We've figured out good chunks of it, however it's proving frustrating given we're piecing things back together.

I was wondering if anybody could perhaps shed some light please.  We have the wiring diagram (which is itself daunting), but does anyone have any diagrams that indicate locations of the harness on the frame and/or the connections to the specific components?

Another option we are looking at is to simplify the wiring (or indeed make a new wiring harness from scratch minus the sub-harness for the ignition side of things).  Has anybody got any experience with this (or a helpful, simple wiring diagram at hand?)

Many Thanks,

Matt

Here's a colored one if you haven't found it yet.  (It's not as complicated as it looks.)

http://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/kwiring/Early%20K75%20K100/K100_Early_Wiring_Diagram.jpeg

If you want, post up some photos of what you have but you will need to state what model K100RS as there are 2v, 2v with ABS, 4v with ABS and naturally the wiring differs.

It should not be too difficult if the wiring you got is in good condition. A few instances occur of identical connectors and components but it can be worked out.

There is nothing like getting someone along who knows the K bikes....a coffee workshop day can work wonders....

Thanks duck and Olaf.

That's the diagram that has blown my mind haha!  I think that the harness being off the bike in the first instance has thrown me.  

That's great, Olaf,  I'll take some photos tomorrow and post them up.  The bike is a 2V ABS model (there is an ABS connection on the harness however we have no ABS module) - whether the harness and the rest of the bike are one and the same remains a mystery for now.

Much appreciated.

The two black,  rectangular multi plugs are for the two computers. The two white shrouded plugs are for the handlebar switches. All solid brown wires are earth. 

There are variations, so verify with wire colour codes. A good bulk of it goes under the tank. The loom has two branches for left and right of frame under tank.  On the left,  from front to back;  the front has two branches - headlight and instrument cluster,  further back three branches at the same point - clutch, choke and hazard switches,  next another four branches - empty (additional instruments)  indicators (+ Parker and horn) EFI (computer under seat) empty (heated grips) Last, left handlebar switch.

On right (front to back) front brake, oil pressure, four pin ignition,  handlebar,  Fuel tank (four pin but five plug) A branch on the right side goes down the frame for rear brake,  speedo and gear position senders. 

Also on right - hall sensor,  ICU (computer)

Maybe label the plugs with masking tape once identified, so you only have to do it once.

If you are trying to figure out how to put the harness on the frame, go to the Portal page and select the technical information in the middle of the page.  When you get to the page with all the resources, open the BMW shop manual and go to section 61 General Electrical system.  About the 3rd or 4th page has a drawing of how the harness is attached to the frame.

Recommendation: Put the main wiring harness on top of the engine before attaching the frame.

Great, thanks for the information!

We've run the harness around the bike so far, but I'll whip it out and place it on top (thanks duck)

Point-Seven-Five, thanks - We have the workshop manual printed out so I'll dig out that page.

daveyson, that's great, thanks!  I think that'll give us a really good idea of where to narrow down the connection points.  I'm back at the bike this afternoon so you've all helped me put a plan together.  Watch this space!

Anton Lagardier's stuff includes a great diagram of the connectors and wiring routing under the tank on a 2v. I can't find any link to it right now, but unless someone can dig one up I'll head for the shed and post a photo of my printed copy later.

Lagardier eh?

Edit, if I'd shown some respect and spelled the guy's name right...Largiader - doh!

Thanks Chris.

daveyson, your info was invaluable in narrowing down where to find things, as such we have found almost everything (green ticks in the photo below).  We have also found the front brake sw, rear brake sw, speedo and gear position senders however I took the picture before labelling the harness and therefore confused myself when adding the red '?'.  Struggling to find the other bits to match the wire colours on the diagram.  If anyone can help further narrow this down based on the attached that would be amazing!  

Thanks everyone - great community here!

Look for a BMW part number somewhere on the loom. It's usually a grey-coloured tag with at least 7 digits, but perhaps the entire 11 digit BMW part number. With that you can the enter those numbers into www.realoem.com/bmw and it will tell you if it matches the frame's year and model.

Once done with that, how 'bout popping over to the member's intro page and doing that, noting you've not done that requirement as yet. Then we can truly welcome you to the forum!

Here's a link: Member's Introduction

Whoops, sorry - will do that now.

Here's a link to a PDF of a K75 factory wiring diagram. Some of the EFI stuff will be a little different  on a 4 cylinder K but most of the wiring is identical to a K100.  The wire color and component names (that I did in English) are text searchable in the PDF file which might make things easier for you.

http://bit.ly/EarlyK75WiringPDF

Hope this helps

The ABS question mark plug looks like the plug for the fuel injection computer, that branch goes down the left side of the bike. 

Yep the colour diagram is intimidating at first glance,  but focus on one part at a time, it will soon be one of your best helpers. 

What year is it?

I should mention..
1 The front of the bike is at the bottom of the diagram.

2 Turns out it wasn’t anything of Anton’s; some guy called Bert Vogel instead. Another hero.

Thanks Chris, that looks like it will be really helpful and I'll have a play with it again tomorrow.

daveyson, it's supposed to be a 1989 but many of the components are also 1985 (the registration document is 1989).  Also, I attached a cropped photo as that sub-harness we had figured out already I believe so I didn't include it.  I've attached it below which I think shows the separate connection for the fuel injection unit (I believe)

The plug without a tick from the ICU multiplug I think will match the hall sensor wire which comes from under the front right side.

mtuttey wrote:. . .  does anyone have any diagrams that indicate locations of the harness on the frame and/or the connections to the specific components?

Go to Chapter 46, pages 63–67 in this BMW manual that is found in the Tech Pages by clicking on the Portal tab at the top of this page. There's a lot of well-organized, useful information in the tech page section.

Thanks everyone - your information so far has been really useful and we seem to have pretty much pieced everything together bar a couple of things (photo below shows that we've mounted the harness on the frame and connected almost everything we have).

A couple of stumbling blocks so far is trying to figure out which is the connecter to the fuel sender if anyone can narrow that one down.

And secondly, which is more of a challenge.  We plan to test run it shortly to see if the engine is working properly.  We don't have any switches or handlebar controls (and we will be installing aftermarket units) - I notice the starter switch is via the R/H handlebar control and I understand that we have to close the clutch switch to start which we can do via the wiring.  Any ideas on how to get the starter switch connected - the two black/yellow wires enter the same terminal in the block (I originally thought by the electrical diagram that these would need to be connected together, however they already are).

Many Thanks,

Matt

If the gear position indicator switch (back of gearbox) is in place, connected and functioning correctly, starting should be fine. For the starter to work its an either/or for gear position indicator showing neutral or clutch lever pulled in.

Bill

It will be best if you attach the right switchgear and then:

Find the  wiring harness connector for the clutch switch and short it (which is all the clutch switch does.) Clutch switch connector has two wires - green/black and black/green.  That sends 12V to the start button.  There isn't a lot of current involved since it just needs enough power to trigger the starter relay.

Otherwise you'll also need to emulate  the start/kill switch by shorting the green wire to the green/yellow wire at the right switchgear connector.  To engage the starter put 12V to the black yellow wired pin at the right switchgear connector.

Fuel tank connector has four wires:
Green/white
Brown
Yellow
White

Hi guys, apologies for the slow response as we had been working hard to get this thing running.  Thanks to you guys for the help as we fired it up a few days ago.  Here it is!

https://youtu.be/hDzIcq2_DAU

Good to see.

Good to see.