Boxerworks.com

Close! I'll have a look at mine to compare.
edit: well, I had a look and for the life of me can't get any image like yours in situ, direct visual or camera. It's busy down there.

Makes me then wonder if something isn't assembled quite right or bent? Sorry, can't give any meaningful help except a review of the assembly procedure.
https://youtu.be/7cy0qUJiqDw?t=333

Anyone have a photo of your rear brake switch setup?

You're right it is busy down there but I think I can see a problem with what you have....

What I think I'm seeing is the top of the brake lever casting towards the top of the page with the switch lower down. The bolt at the top is threaded into the top of the lever and, when the brake is off, comes into contact with the metal bracket attached to the frame. The actuating plunger for the brake light switch protrudes through a hole in the bracket.

If my view is correct than there is an obvious problem (or indeed a couple).

1) The aforementioned bolt isn't the right one. The correct bolt has a slightly domed head. This may or may not have a bearing on your problem.

2) The bolt doubles as the height adjusting stop for the brake pedal in the off position and as the actuator for the brake switch. It should align with the switch plunger and, as the lever returns to the off position, it should press the plunger turning the light off.

In case you haven't worked it out... the switch is a 'Normally on' switch which is on when the plunger is extended and off when it is pressed in.

In the your picture the bolt is not aligned with the switch plunger and will never press it in...

Which brings us to...

3) If the plunger is never being press by the lever, then in principal, the brake lamp should be constantly on... which, if my understanding is right, it isn't... so that implies that there is something else wrong with the circuit, possibly a faulty switch or wiring but also possibly something done by a previous owner to prevent the brake light being permanently activated.

Recomendations:

a) Replace the stop bolt with a suitable substitute. If you can source an original, so much the better. If not, grind a suitable stainless bolt so the head is slightly domed. Use stainless because you will destroy the rust resistant coating on anything else and it will rust in that location.

b) Find out why the bolt head is misaligned with the switch plunger. From the image it looks like the lever is twisted but I can't be sure. If the lever bearing is badly worn, that can be enough to pull the lever to one side. If the bearing is twisted, be very careful in twisting it back... alloy doesn't take kindly to a lot of twisting and can crack or break.

c) Track down the electrical problem...

i) disconnect the twin connector located near to the right rear downtube on the frame. With the ignition on, short the connectors in the (loom side) of the connector together. If the lamp lights up, the problem is towards the switch. If it doesn't, there is a supply problem on the loom side of the circuit.

ii) If the lamp lights in (i), then go to the switch. At this stage, it's a good idea to remove the switch from the bike. This is MUCH easier if the rear wheel is removed. The switch is held to the frame bracket by two screws with heads under the rubber cover. The wires connect with screw connectors (also under the cover)

iii) test the wiring by shorting the two wires removed from the switch (having reconnected the twin connector). If lamp lights, the switch is defective... if it doesn't then the wiring between the double connector and the switch is broken.

iv) assuming the wiring is proved good, then the switch is bad. You'll probably need to replace it but it's worth giving it a dousing in electrical switch cleaner (NOT WD40!).

OK, hope that helps get to the bottom of it. Keep us posted.

Rob

eriojas wrote: ↑Fri Apr 04, 2025 9:56 pm My 1979 R100Rs, cant align rear brake pedal with the switch activator, so brake light stays on always, is there any way to adjust the brake pedal mechanism ? The switch has a fixed bracket , no adjustment

I would 'adjust' it with a strategically placed hammer blow.

Thks Rob, its exactly as you described, the brake light is always on, if I depress the plunger it goes off, so the switch it works perfectly, the brake lever bolt is misaligned, the bolt you mention is the right one has a thicker head, as you also say, if the brake lever is bent, trying to bend it may break it, maybe a big washer that pushes the plunger may work, will try to find the right bolt

Your description is great, are you some kind of writer??

Will keep n you posted thks again!!

A strategically positioned blow might work!!

The brake lever is cast so is in danger of snapping. Removing the lever is easy enough. Can you do that to inspect and maybe post a picture? If you use some strategic brutane with a solid tool, it'll be safer and easier off the bike.

If all else is good then a McGuyver fix might be to change that bolt head so it's wider and presses the switch plunger. A spot weld to the top of the nut or a nut with a wider head?

Hopefully you can get away with it without breaking and replacing it. It won't need to move far though if you whack it. Fingers crossed.

Maybe the correct bolt will do the job.
The one in this picture is different to the one in yours.

pn 35 21 1 231 067 HEX BOLT - M6X20-8.8ZNS3
Shouldn't be hard to source locally.

thks steve, will try to source it and see if that works