Last autumn I took off the old battery on my 1990 K100RS with the intention of replacing it .   Got a new battery a short while ago , put it on then found I had a blue wire with a battery terminal one end and spade connector the other , its  about twelve inches long so this restricts where it goes to ( possibly alternator ?) but can I find where the spade connector goes , NO .     Sorry for this pathetically simple question but it has me stumped.   Any thoughts please ?

Is there a blue wire connected to the alternator?  Pretty sure that's where it should go.  I just don't understand why it goes directly to the battery positive terminal.

Guess it must be original brown, earth.
1 end goes to - , the other on the housing of the computer.

Post a picture of the wire to make sure its OEM and not aftermarket.

Thank you for these thoughts , I will have another look today and see if I can come up with the answer .   I do have a picture of the wire but as I am a bit of a "Dinosaur"  , not sure how to post it

Is there a blue wire connected to the alternator?  If not, that may answer your question.

Thank you all for your help here and it DOES go to the alternator .    Got the bike outside in much better light and after removing everything including the battery , found the "spade" connector on the end of the Alternator .  I have a terrible thing to admit though !!!!!  The offending wire was Black not Blue as I stated . Sorry 

The problem now is that the wire in question doesn't go to the battery.  In the wiring drawing, it looks like it goes to the instrument cluster.

Should have enough posts to upload a piccy now. Problem as I see it is that it can't be an OEM wire because BMW only used black to connect up the water temp sensor under the oil/water pump at the front. It's a blue wire from the alternator to the instrument cluster.

Cut the green wire they said...
It will be fun they said....

There could be a black earth wire from the battery to gear box, above the shift lever.

Just for the record; the K100RS is a 8V or 16V ?

That's a brown wire hiding in a black coat!

Dai wrote:That's a brown wire hiding in a black coat!

That cheecky bastard !