Brake fluid reservoir wires

[Chuey]

OK, I just learned that I don't know how to spell reservoir without spellcheck. And I love that spellcheck isn't a word.

Now, on my R90S which started out as a 1974 R90/6 but has had a dual disc setup added, from the same generation, I have a wiring question. The master cylinder (under tank model) has two wires on the cap. I know those wires are for the fluid level warning light on the dash. Mine also has what appears to be a brake light switch on the front of the M/C facing forward.

My front brake lever has a brake light switch mounted on it (stock). When I put the bike together, I put the two wires from the wiring loom onto the brake light switch of the M/C. The light has always been on but I knew that the brakes worked and assumed there was something amiss in my wiring loom. Today, I'm making some changes in the bike and have the tank off. I'm thinking that switching the wires from the M/C brake switch to the fluid level prongs on the cap will make the only wiring glitch go away.

This kind of illustrates to me that with the admirable amount of interchangeability these bikes have, sometimes it can get you.

I'm wondering which bikes used the switch on the front of the master cylinder under the tank.

Chuey

[George Ryals]

I think when the handlebar controls changed is '75 the front brake light switch went to the m/c. You can test your wiring change to the cap by lifting the float under the cap to see if the light goes out.

[DanielMc]

Chuey - when you say "The light has always been on but I knew that the brakes worked and assumed there was something amiss in my wiring loom" I'm not entirely sure which light you're referring to.

The brake fluid level warning circuit runs a blue/brown wire from the warning light in the the instrument console to one side of the level switch on top of the reservoir. The other side of the switch is joined into a common earth via a plain brown wire. When the fluid level drops the blue/brown wire gets earthed onto the common earth. If it's the instrument console's brake fluid warning light that's on continuously then that circuit has nothing to do with the brakelight switch, and is easily sidestepped by just removing the blue/brown wire from the cap - the plain brown wire is part of a bigger earth circuit and needs to be left alone. The front brake warning light should work whether wired from either the early type handlebar switch or the later type pressure switch on the MC - either way it operates by completing the live side of a circuit and is fed in either case by a green/red wire and a green/black wire.

[Chuey]

Hoowee! Now I'm really cornfused. Within a day or two, I should have the bike all together again and then I can check what I did with the wires. The light that was on is the one at the top of the center cluster between the gauges. I'm pretty sure I just hooked up the wires that were supposed to go to the fluid level tabs on the M/C cap to the wrong place. Thing is, it would seem that if the light was on all the time, it would have gone off when the switch got pressure. It's sometimes embarrassing to be this dumb about electricity.

Chuey

[Chuey]

OK, I realized when typing that last post that I could check the bike now even though it's not ready to run. I've been changing the handlebars and switched to some rearsets that I bought about a year ago. The rearsets went well and I can't wait to try them, as the originals are too far forward when you really gas a bike like this one. It doesn't lend as much control as it accelerates and pushes me back in the seat. I'm thinking the new foot position will allow me to push back instead of feeling passive.

I'm also changing the handlebars. That sounds easy but I've had a heck of a time with the wires. Good news is that I'll not be bothered by the little red light unless I run low on brake fluid. (Got that sorted, thanks.) Not, the mystery is that the right signal is on even when the switch is in the off position and moving the switch does nothing else. I had the switch removed from the bar and from the mounting part so I may have munged up some wires in there. It will be nothing but fun to try to sorth that one. It worked before so it should be within my ability.

Chuey

[Deleted User 72]

It worked before so it should be within my ability.

Chuey

Not to rain on your parade... but the above is fawlty logic.

I spent several months beating on my alternator being beaten by my alternator following the fawlty thought. Adding Frankham's Ground Wire fixed it like magic.

edit: I meant to say "Frankham's Earthing Loom" fixed it like magic. (Thx, Dan.)

[DanielMc]

Adding Frankham's Ground Wire fixed it like magic.

I've said it before - he's a national hero in the UK. Here's a portrait of the great man undertaking an early experiment entitled "Attempting To Improve The Efficiency Of The Airhead Earthing Circuit"

[Chuey]

Did Sir Robin do experiments that made women look away and put fearful looks on the faces of children? Now, that's cool!

Chuey

[DanielMc]

Did Sir Robin do experiments that made women look away and put fearful looks on the faces of children? Now, that's cool!

Chuey

That's what happens in my house when I pick up spanners - I thought it was normal...

[Armaguidon13]

As my idiot light doesn't work on my R90 turn signal, you made me thinking of usint the brake fluid idiot light