Boxerworks.com

Any help is very much appreciated.
1975 R906
I have recently had a meltdown with my original left side switches (horn, headlights). I purchased a replacement and there are extra wires and the wire colors do not match the original part. When I inquired about this, it was explained that in 1978 BMW changed the part number and the original part number was superseded.
I’ve been told and I am sure sure that I can use the new part, but I have no idea how to wire the “new” part.

Welcome to the forum, Snapper.
Hmm, Haynes manual shows a lot of variations to the wiring in the 75 to 78 period with a change from 9 wires to 10 wires to 11 wires from the left side perch. Probably best to get hold of the Haynes manual (wiring diagrams are in colour) and nut it out. You could also use a multimeter with a continuity beeper to test each circuit. Good luck.

Some of it depends on whether you have a new switch that is for the US and is set-up for "Headlight ON all the time" or someplace else where that is not required, or you still are permitted an OFF function.
Best way to deal with this is to have an original schematic and a schematic that represents the new unit. Then ID the new schematic using the old schematic for a guide. Some wires may not be used!

The wiring looms for R90/6s, changes sometime in 75, the easiest way to check which loom you have is to see if there are earth wires to the front indicator switches. My June bike has the earlier wiring loom.

So, snapper needs to tell us the MONTH and year of production of his R90...
It's on the metal tag on the steering post (or ought to be.)
Do you have a HEADLIGHT RELAY? That changes things too.
OLD Clymer schematics sorta hint at this mess...the wiring colors changed from the 1974 R90S to the 1975 R90S.
Another source I have shows the DIN colors were revised in 1975 so that's the answer for that. Nice to know, isn't it?
(They also messed around with the wiring for the clutch switch (starter-permissive) so the plain-brown wire might go to some sort of connector rather than being just a plain brown wire.)
Of course the really nasty thing is that by 1978, there were no NEW R90's so "replacement parts" in 2012 are just that...Field-Fiddle-Fit. We CAN DO IT. Hang in there.
Have you got schematics?

Officially the wiring will have changed from sept 75, but checking the loom is the best way.

Wonder if snapper went to the Bahamas, too?

Jean wrote:Wonder if snapper went to the Bahamas, too?

Aha! The plot is thickening nicely.

Perhaps the opportunity for a romantic misunderstanding will present itself over a chance discussion about BMW electrical issues.

Or is he (?) wandering about in the Atlanta airport...
I hate it when someone drops off the earth without a whimper while we are working our fannys off to help solve their problems.
I'm going for a beer.

Jean wrote: I'm going for a beer.

That's the spirit, Jean. Bit early here, but I'll join you when the sun's over the yardarm.