So from my reading on here and elsewhere, I've come to the conclusion that a new sensor for an aftermarket speedo is required. I don't want to, but i've accepted that.

I've assumed I'll be able to, and am willing to trial making warning lights using existing circuitry and a little chopping and chasing. Progress will be detailed in my build thread.

So my main question is (assuming no one has any major contradiction to my above two comments), how do I wire in an aftermarket RPM gauge, either digital or with analogue needle? I haven't decided on the style I'd like yet, and I guess the answer to this question could dictate that.

Is there a fitted sensor that is compatible, or is it a case of adding another sensor to the gearbox or such like?

Many thanks in advance!
Jase

If you use an Acewell 2853 for the RPM you can either connect the wire to the existing (Black Blue) wire feeding the speedo for RMP. Or run the wire down to the ignition coil and take a few turns around it. I suspect other digital gauges will be similar but have not really looked. 

Acelwell
https://s38.photobucket.com/user/green_bread/media/AcewellTachWiring.jpg.html

You can also get most of the warning lights working, Oil, water, indicators, high beam. The only weird one with the Acewell is the fuel gauge. It will read empty until your fuel light would usually go on then it will read full so you still get some sort of indication.

What are you trying to get working?  Is it the speedometer using the BMW speed sensor?  Or is it the tachometer using the tach signal from the coils?  

If the  former, the OEM sensor will not work. Acewell supplies a magnetic sensor that attaches to the front wheel that will give you a functioning speedometer.  If it is the latter, rapt gave the answer above.

The fuel level sender can be modified to work with Japanese style fuel gauges.  Search for "Messing with the Fuel sender" in this site for details.

Most of the indicators are straight foward - turn signals, high beam, oil pressure, over temperature, choke, BMU.  Neutral light requires you to build an additional relay circuit to function though.

I knew about the speedo issue, and now I know how to go about getting the rest tapped in. 

Thanks guys! My main concern was the rpm gauge!

Cheers

Edit: that ace well gauge has been updated to this model: http://www.acewell.co.uk/Acewell%20Speedometers/ACE-2xxx/ACE-2856+Plastic_case.htm?action=full&id=18

At the bottom of the page is a speed sensor option, which one would be appropriate for my bike?
Thanks

Oooooh this is nice!

http://www.acewell.co.uk/Acewell%20Speedometers/ACE-4xxx/ACE-4554CP.htm?action=full&id=43


Thoughts?

JaseYPK wrote:I knew about the speedo issue, and now I know how to go about getting the rest tapped in. 

Thanks guys! My main concern was the rpm gauge!

Cheers

Edit: that ace well gauge has been updated to this model: http://www.acewell.co.uk/Acewell%20Speedometers/ACE-2xxx/ACE-2856+Plastic_case.htm?action=full&id=18

At the bottom of the page is a speed sensor option, which one would be appropriate for my bike?
Thanks

Go for the Plastic reed switch. 
See post number 6 on my build for a really simple bracket for this type of sensor.
https://www.k100-forum.com/t9009-rapt-s-1986-k100

Awesome thanks, had a look at your build thread and your bikes looking sweet!!!

anyone have a simple wiring diagam for acewell guauge to suit k100 85  im looking for a diagram that tells me which wire on bike loom does what function 

i also have a long earth strap metal with3 connections points i assume mid point goes to frame earth but where do the other ends connect 
thanks David

Try this, sorry only in geman language,
but in the end the lines are right :-)

Cheers

Click on the image to see the forum post:

Espresso, Is that the schematic for Maru's Brotbox v2.0 from FlyingBrick.de??

Hello Robert!

Indeed, it is from Maru Swiss Page.
This is the full link: 
http://maru-labs.com/wp-content/uploads/2015/10/BEP2_Anleitung.pdf

Cheers

Cheers!!! Thanks for the link.