K11 Owners Group

[BB]

Rear brake light works (foot), but the front brake light is inop (hand). Is this more than likely a connector problem or a bulb monitoring device problem? I have the wiring diagram and am not sure where the bulb monitoring device is located. Anyone experienced a similar problem? Any help would be appreciated. Oh its a '93 LT
_________________
93 K11LT
74 R90/6
78 R80/7 In "RS" Clothing
1957 NSU Superfox

[Flying Duck]

Most likely a bad switch.

The BMU is in the relay box under the tank. It's on the rider's left side and is black. If you remove that, you can test for an input from the front brake switch. The gray/red wire should be 12V when the front brake is applied.
_________________
93 LT (x2)
94 RS
86-97 K75F(K75/100/1100 Frankenbrick)
86 K75C w/paralever, hi perf cams,TURBO!
91 & 92 K75Ss
91 K1
86 custom K100
14 WR250R
IBA #17739 (SS1K, BBG, 50CC)
Buy parts HERE

[BB]

I'll check that out. Am I correct in assuming that the ABS is non functioning as long as the BMU is picking up the switch failure or......?
_________________
93 K11LT
74 R90/6
78 R80/7 In "RS" Clothing
1957 NSU Superfox

[Flying Duck]

ABS only senses wheel rotation (or lack thereof) and is not connected to the brake switch in any way. If the ABS light in the lower part of the speedo isn't blinking then your ABS is operational.
_________________
93 LT (x2)
94 RS
86-97 K75F(K75/100/1100 Frankenbrick)
86 K75C w/paralever, hi perf cams,TURBO!
91 & 92 K75Ss
91 K1
86 custom K100
14 WR250R
IBA #17739 (SS1K, BBG, 50CC)
Buy parts HERE

[BB]

I thought that the brake light working was a part of the ABS system. The BMU is included in the ABS schematic. I typically get a front wheel sensor light on the ABS codes, and can clear it. I have a blinking ABS light after that code is cleared, and no other codes present. I assumed that it was the front brake switch (?) failure that was keeping the ABS flashing, and most likely not functioning. Any thought? Buy the way........thanks for your help.BB
_________________
93 K11LT
74 R90/6
78 R80/7 In "RS" Clothing
1957 NSU Superfox

[Flying Duck]

Here's the pinout for a 93 ABS brain. Notice no wires connect to the brake switches.

Pin Wire Color To
1 Coax/Ground Front Sensor
2 Green Front Sensor
3 Coax/Ground Rear Sensor
4 Yellow Rear Sensor
5 Black ABS Switch
6 Black Front Modulator
7 Black Rear Modulator
8 White/Blue BMU/Lamp
9 Brown Front Modulator
10 Red Front Modulator
11 Brown Rear Modulator
12 Red Rear Modulator
13 Coax shield Rear Modulator
14 Brown Ground
16 Green Ign Switch
17 Brown/Yellow ABS Relay
18 Red/Black ABS Warn Relay
19 Brown/Red ABS Relay
23 Brown/White Diagnostic Plug
25 Coax shield Front Modulator

There is one that connects to the BMU bulb (blue/white). I'd always thought that was to make the BMU light flash but I suppose it's possible that the ABS brain monitors it. But that would mean that a bad tail light bulb would cause the ABS to fault too which doesn't make sense.

On my 94 RS, I got rid of the BMU to run LEDs and wired the BMU light up as a side stand down warning lamp. Even with that light lit the ABS will still initialize properly when I ride off.

ABS is all Voodoo anyhow.

Is your ABS light flashing when you're riding?

Have you checked the spacing and connector for your front ABS sensor?
_________________
93 LT (x2)
94 RS
86-97 K75F(K75/100/1100 Frankenbrick)
86 K75C w/paralever, hi perf cams,TURBO!
91 & 92 K75Ss
91 K1
86 custom K100
14 WR250R
IBA #17739 (SS1K, BBG, 50CC)
Buy parts HERE

[BB]

The rear light monitor stays lit (solid) and the ABS light flashes. It never gets past that sequence. I believe the bulb sensor is the first check on the ABS circuit. Once it determines the front and rear brakes are functioning it should go to both flashing....then clear at 2-3 mph. I will check the front wheel sensor as it may be part of the problem. I havent checked for 12v yet at the BMU, but that will be the next test. It sounds like I may have 2 different problems. Thanks
_________________
93 K11LT
74 R90/6
78 R80/7 In "RS" Clothing
1957 NSU Superfox

[Flying Duck]

I've removed the bulb monitors from both of my bikes (to run LEDs) and the ABS works fine. The way I have things wired it is IMPOSSIBLE for the ABS brain to know if I've applied the brakes or not. The tail light wire is wired directly to the fuse. The brake light is wired directly to the switches. The BMU bulb is wired to my side stand switch and the ABS initializes fine whether that light is on or off.

The ABS does not monitor your brake switches. It doesn't make sense for ABS to fault if a brake switch or tail/brake light bulb goes out. That would be a pretty bad design in my book.

It can sense a wheel lockup from the pulse rates from the sensors. That's all it needs to know.
_________________
93 LT (x2)
94 RS
86-97 K75F(K75/100/1100 Frankenbrick)
86 K75C w/paralever, hi perf cams,TURBO!
91 & 92 K75Ss
91 K1
86 custom K100
14 WR250R
IBA #17739 (SS1K, BBG, 50CC)
Buy parts HERE

[Mystic Red]

Have you checked the sensor gaps yet? I'm with Drake, ABS doesn't care if the bulbs work.
_________________
Scott Hespelt, '94 K11LT
K11 OG #466

[BB]

Woahhhhhhhh, I'm pulling my hair out. I decided to track down one problem at a time. I'm trying to trace the problem with the hand brake light. I have 12v at the BMU gray/red wire only when I apply the rear brake. Same for the foot brake wires 12v at the gray/green wire at the BMU.Traced all the wires I could and checked for continuity...all good. The front brake switch seems to be working, leads to the tail light ckeck OK. I cant see the forest for the trees, any ideas? Whats the best way to bypass the BMU? Does it make sense that I would have the rear brake lighting up on the front brake circuit? I removed the radio and alarm just before this started. I wouldnt think there would be a connection there. Am I right or wrong? Thanks for any help. BB
_________________
93 K11LT
74 R90/6
78 R80/7 In "RS" Clothing
1957 NSU Superfox

[Flying Duck]

Get rid of the BMU:
http://smithduck.home.comcast.net/~smithduck/bmw/tech/bmu/bmubyebye.htm

Remove the BMU from it's connector. Put a probe in the connector terminal for the gray/red wire to be sure the front brake switch is working.

Have you removed the instrument cluster recently? If you misalign the pins on that it can fry the BMU.

Stereo and alarm removal should have no impact on BMU operation.
_________________
93 LT (x2)
94 RS
86-97 K75F(K75/100/1100 Frankenbrick)
86 K75C w/paralever, hi perf cams,TURBO!
91 & 92 K75Ss
91 K1
86 custom K100
14 WR250R
IBA #17739 (SS1K, BBG, 50CC)
Buy parts HERE

[BB]

Thanks Drake. I pulled the connector to the front brake switch and looped it......got power at the BMU....switch must be bad. It also let the brake monitor light flash.....should be on the way to fixed. Thanx again
_________________
93 K11LT
74 R90/6
78 R80/7 In "RS" Clothing
1957 NSU Superfox

[BB]

New switch and everything is back to normal...Brake light and ABS. Thanks for all that good help.
_________________
93 K11LT
74 R90/6
78 R80/7 In "RS" Clothing
1957 NSU Superfox