Vintage BMW Motorcycle Owners

Hi Guys,

I've just taken ownership of a 1973 R90/6 complete with Velorex Sidecar. Currently preparing it for RWC and I'm pleased to say it's not too far from ready. I am trying to chase the front brake pressure switch wiring as it is missing IE no obvious wiring hidden or disconnected from the pressure switch at front of master cylinder. It has a factory option twin disc and the pressure switch is present however i cannot find any orphaned wires which may have been the original connections.
i understand there's a connector block from the schematic diagram however i cannot find it's location? (i haven't disassembled headlight assembly as yet. If anyone could throw some light on this i'd be appreciative .

Regards Graeme

I'm sure you're deep into the bike! BTW...I'd probably call is a '74 R90/6...it might have been built in 1973 but likely it's a 1974 model. But that's just my opinion!

I think I might have found the wires involved. I've looked on the wiring diagram for my R100/7 which should be the same. It lists a "hydraulic hand brake switch". I has two different wires coming from it. One is a green/red wire and it heads back to the rear brake light. Once the hydraulic switch closes, power goes down the line to the rear brake light. The other terminal has two green/black wires. One wire goes to the rear brake pedal switch. The other wire goes to one side of the 8A fuse at terminal 15 in the headlight. Power is going through the fuse and goes through both of these switches. Grounding for the brake light should be at the light itself.

I think this is the wire for it:

https://www.euromotoelectrics.com/produ ... har767.htm

It's got the right colors but I don't recall that plug connector the last time I was working on my master cylinder.

Good luck with your preparations!

Thanks for the detailed reply Kurt. Reg papers say it's a 73, it also has twin discs which I believe was a factory option. I'll pop the headlight out tomorrow and see if I can trace the wires you mention.
Regards Graeme.

I am adding this and it may or may not help. Check on the right side of the frame, near the steering head for a block plug with the proper color wires. It might be the previous owner disconnected the brake pressure switch there and connected the plugs together. LOL, sorry, I don't have pictures and a I have a poor memory as to exactly what to look fore. I give this advice as my RT had a plug set up like what I describe. St.

Gadget,
Check for a front brake light switch on the perch for the throttle/brake lever. That is how my 74 R90/6 is set up.
I suspect that a previous owner may have changed out the under tank master cylinder for a dual outlet unit when the second disc was added. If it was from a later bike it would have the switch at the master cylinder and they left it in place to plug the hole.
Just a theory.
Brett

My R 90/6 is a 1975. It has the master cylinder is mounted on the handle bar. The brake light switch works off the lever and is mechanical rather than hydraulic. As per the attached photo. (If I successfully attached it.) I also attached a wiring diagram.

Craig

Sorry - That photo was really washed out. This one should be more visible. Notice that the brake light switch is on the lever in front of the master cylinder. BTW the color code of green and red to the light, red and black to power is the same on my '71 R 75/5 so I think it would be the same on yours.

Craig

EME sells a very good large color, numbered matted plastic wiring diagram, one of the best on the market. St.