BMW K bikes (Bricks)

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1Back to top Go down   Brake light on all time Empty Brake light on all time on Fri Jan 31, 2020 12:06 am

Packo

Packo
Silver member
Silver member
I really struggle with electrics !!!
My brake light comes on with the ignition and stays on all the time until the ignition is switched off.
The RED warning light on the cluster operates as it should ie. OFF once each of the brake switches are operated
With ignition ON I have power to both wires at the rear brake switch all the time so that appears to be the problem.
What are the steps to try to track down the "short" ??
I have checked the earth wires under the tank and as they are bundled together and all other functions on the bike are normal I don't see how it would be there.
From here do I go to the BMU and if so what do I check and how


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83 K100 HRD Outfit
77 R100RS
1992 K1100 Outfit
1983 K100
    

2Back to top Go down   Brake light on all time Empty Re: Brake light on all time on Fri Jan 31, 2020 12:36 am

Laitch

Laitch
Life time member
Life time member
The first thing to do—although now it's the second or third— is go to the brake pedal and view how it activates the switch there. It's a plunger switch and it might be stuck inward and in need of some cleaning and convincing to release outward, or it might need replacing altogether. Attached is an example from Euro Motoelectric. Also, inspect and clean the switch wire's harness connector, too.
Brake light on all time K100_r11


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1995 K75 73,000 miles
Brake light on all time Usa-lo10
    

3Back to top Go down   Brake light on all time Empty Re: Brake light on all time on Fri Jan 31, 2020 6:23 am

duck

duck
Life time member
Life time member
Yes, the BMU connector is a good place to troubleshoot. (But a PITA to get to.)

Take the BMU out and then test the following at the connector:

The Gray/Red wire should only have 12V when the front brake switch is activated.

The Gray/Green wire should only have 12V when the rear brake switch is activated.

However, what I would do first (because it's easiest) is disconnect the rear brake switch connector under the right battery cover (gray/green and green/black wires) to see if the brake light goes out when you disconnect that. If that makes the brake light go out then you have an issue with the rear brake switch.


With the BMU disconnected, shorting from the gray/red wire (front brake switch) to the gray/yellow wire (brake light) should light up the brake light. Shorting from the gray/green (rear brake switch) to the gray/yellow wire should light up the brake light.  If both of those work with the BMU disconnected then your BMU is bad.


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Current stable:
86 Custom K100 (standard fairing, K75 Belly pan, Ceramic chromed engine covers, paralever)
K75 Frankenbrick (Paralever, K11 front end, hybrid ABS, K1100RS fairing, radial tires)
86 K75C Turbo w/ paralever
94 K1100RS
93 K1100LT (x2)
91 K1
93 K75S (K11 front end)
91 K75S (K1 front end)
14 Yamaha WR250R
98 Taxi Cab K1200RS
14 K1600GT
http://www.ClassicKBikes.com
    

4Back to top Go down   Brake light on all time Empty Re: Brake light on all time on Fri Jan 31, 2020 6:45 am

92KK 84WW Olaf

92KK 84WW Olaf
Life time member
Life time member
Same problem on my RS...but heres how I solved it.

I got this 83 RS about a year ago after it sat a long time.

Working through it realised it needed lots, one of the things being brakes overhaul. All done, but bulb warning light on, replaced switches and solved.....but brake light on all time.

Narrowed it down to rear by turning on ignition and noting the warning triangle would go out as normal by using front brake only > problem is somewhere in rear brake. 

Further investigation revealed the pedal was not making contact with the brake switch pin. There is an adjuster on the pedal just below the brake switch.....but also my spring for the brake pedal went walk about. As I know from a trip to France with 88 some years back, no spring the pedal sags and brake light on all the time.

A no cost fix. Just lift the pedal up while the ignition is on and see if the brake light goes out......


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1992 K100LT 0193214 Bertha Alaska Blue 101,000 miles
1984 K100RT 0022575 Brutus Baja Red 578 bought 36,000 now 89,150 miles
1997 K1100LT 0188024 Wotan Mystic Red 689 58,645 now 102,50 miles
1983 K100RS 0011171 Fricka 606 29,495 miles Damn K Pox Its a Bat outta Hell No 34,600 miles
    

5Back to top Go down   Brake light on all time Empty Re: Brake light on all time on Fri Jan 31, 2020 2:26 pm

MartinW

MartinW
Life time member
Life time member
You also need the correct tension spring. mine was too light and every time I hit a decent bump the brake light would flash on.
Regards Martin.


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K75s Hybrid
    

6Back to top Go down   Brake light on all time Empty Re: Brake light on all time on Fri Jan 31, 2020 7:21 pm

K75cster

K75cster
Life time member
Life time member
Hows it going Packo? Have you disconnected the brake light switches yet, the back brake switch connects under the battery cover and is a sight easier to get to than the front that requires the tank be shifted. If you disc them and it's still on then the BMU needs checking as DUCK said. With the ignition on and the park light on it will have power, it's green black and the stop light wire is green yellow and only has power when a brake switch is activated via us using the brake lever or dirt's stopping the switch pin from moving out free and stopping power.
Grey Green rear brake switch to bmu and grey red front brake switch to bmu.

Hope it's solved. It's the 83bm you're talking about right?


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Keith - 1987 K75c with r100rt replica fairing and half of a 1984 K100rt 1992 K1100LT a blue one

The Clever are adept at extricating themselves from situations that the wise would have avoided from the outset - QUOTE from david Hillel in Out of the Earth.
    

7Back to top Go down   Brake light on all time Empty Brake light on all time on Fri Jan 31, 2020 11:24 pm

Packo

Packo
Silver member
Silver member
[quote="duck"] Yes, the BMU connector is a good place to troubleshoot. (But a PITA to get to.)

Take the BMU out and then test the following at the connector:

The Gray/Red wire should only have 12V when the front brake switch is activated.

The Gray/Green wire should only have 12V when the rear brake switch is activated.

However, what I would do first (because it's easiest) is disconnect the rear brake switch connector under the right battery cover (gray/green and green/black wires) to see if the brake light goes out when you disconnect that. If that makes the brake light go out then you have an issue with the rear brake switch.[quote="duck"]

I did the above checks as suggested : Grey/Red wire had 12V all the time
                                                     Grey/Green only 12V when rear brake switch activated
With these results I then disconnected the front brake switch connector under the tank & the brake light went out
Confirmed that it was definitely a faulty front brake switch and now have a new one on order

Thanks to all who replied for your help


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83 K100 HRD Outfit
77 R100RS
1992 K1100 Outfit
1983 K100
    

8Back to top Go down   Brake light on all time Empty Re: Brake light on all time on Sat Feb 01, 2020 2:28 pm

Point-Seven-five

Point-Seven-five
Life time member
Life time member
In the meantime you might want to soak the front brake switch with penetrating oil.  I had a problem with my "choke" switch, and that got it loosened up again.


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Present:
1994 K75RT
1991 K100RS
1988 K100RS SE

Past:
1994 BMW K75S
1992 BMW K100RS
1982 Honda FT500
1979 Honda XR185
1977 Honda XL125
1974 Honda XL125
1972 OSSA Pioneer 250
1968 Kawasaki 175
    

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