BMW K bikes (Bricks)

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1Back to top Go down   Brake light cutting off engine!!? Empty Brake light cutting off engine!!? Sun Oct 13, 2019 5:17 am

Egilchrist

Egilchrist
New member
New member
HI Guys,
New on here but have had bikes for 40 yrs and this one has me a bit stumped.
1991 K100 RS 16 v completely stock

When activating either brake stop lamp comes on without engine running,little dull for the first 3-4 activations and then brightens up to what you would expect.
Engine running, activate either brake, cuts out instantly.

I have
1.Cleaned up all earths and bulb contacts.
2.put a test lamp across contacts ,all good even with engine running ,(possible resistance discrepancy?)
3.switches appear ok,but its doing the same thing on both,so have ruled that out for now.
4.fuses all seem to be ok,and everything seems to reset after the engine cuts off and will restart as normal.

I am left with thinking it is the BMU gone,but I am a bit old school with electrics so any suggestions or enlightenment would be greatly appreciated.

Thanks in advance.(This problem is almost Italian (ducati) in nature,no offence to all my Italian friends!)
Eric

    

2Back to top Go down   Brake light cutting off engine!!? Empty Re: Brake light cutting off engine!!? Sun Oct 13, 2019 11:07 am

Laitch

Laitch
Life time member
Life time member
@Egilchrist wrote:When activating either brake stop lamp comes on without engine running,little dull for the first 3-4 activations and then brightens up to what you would expect.
Engine running, activate either brake, cuts out instantly.

I am left with thinking it is the BMU gone, . . .
It could be possible to test that hypothesis by following guidelines found in this thread .


__________________________________________________
1995 K75 81,000 miles
Brake light cutting off engine!!? Usa-lo10
    

charlie99

charlie99
VIP
VIP
had a mate with similar issues

turned out to be  the top shock absorber mounting bolt - nut assembly crushing the cabling going to the rear lamps

so have a good examine of that area ...before you do anything else


good luck


__________________________________________________
cheezy grin whilst riding, kinda bloke ....oh the joy !!!! ...... ( brick aviator )

'86 K100 RT..#0090401 ..."Gerty" ( Gertrude Von Clickandshift ) --------O%OBrake light cutting off engine!!? Au-log10

'86 k100 rs.. #######..  "Fred " (f(rame) red ) ( Fredrick leichtundschnell ) - -
bits and pieces from many kind friends across the k100 world ...with many thanks ..
    

4Back to top Go down   Brake light cutting off engine!!? Empty Re: Brake light cutting off engine!!? Mon Oct 14, 2019 10:17 am

RicK G

RicK G
admin
admin
Been thinking about this since I read the post earlier today and it has me intrigued. I recon it will be something like Charlie has suggested.
One of the places that gets chaffed is around the steering head and one other is the pink resistance wire for the heated grips gets overheated and melts the surrounding wires usually in the same area.


__________________________________________________
"Man sacrifices his health in order to make money.
Then he sacrifices money to recuperate his health.
And then he is so anxious about the future that he does not enjoy the present; the result being that he does not live in the present or the future; he lives as if he is never going to die, and then dies having never really lived."   Dalai Lama


Bikes 1998 K1100 LT, 1993 K75 RT, 1996 K75RT, 1986 K75 GS, 1979 Z1300 Kawasaki
    

92KK 84WW Olaf

avatar
Life time member
Life time member
OK been following this one and going to ask a few questions.....

Both brakes kill the engine.....but I can't see how chafing at rear shock and shorting can kill it.

But I can see that if on activating one brake power also feeds into the other brake switch wiring......and the problem is up at the headstock shorting into some other wires.....such as ignition wiring. Tricky because I have been in the wiring on a few Ks and the brake switch wiring is generally well separate.

One little thought I have is that if its an ABS model either a movement of a brake line or a wiring short from the ABS wiring could cause the problem?

The brake light brightening after 3-4 applications is strange.....earthing issue?


__________________________________________________
1992 K100LT 0193214 Bertha 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 106,950 miles Deceased.
1983 K100RS 0011171 Fricka 606 Alaska Blue 29,495 miles Damn K Pox Its a Bat outta Hell Now 37,190 miles. 
1996 K1100LT 0233004 Lohengrin Mystic Red 38,000 miles currently 39.885miles.

Past:
1968 Yamaha 80 YG1
1971 Yamaha 125 YAS-1
1968 Honda 125 SS
1970 Honda CD 175
1973 Honda CB500-4
Honda CX 500
    

6Back to top Go down   Brake light cutting off engine!!? Empty Brake light prob Mon Oct 14, 2019 11:50 pm

daveyson

daveyson
Life time member
Life time member
If the tail light is removed,  check if the dimness problem disappears. Maybe check if you have 12 Volts at the positive of the brake light with the dim problem, and also for 12 Volts at the negative.


__________________________________________________
11/1985 bmw k100rt (late model)  Vin. 0090567
 ~120,000 km
    

7Back to top Go down   Brake light cutting off engine!!? Empty Re: Brake light cutting off engine!!? Tue Oct 15, 2019 10:22 am

Poupy

Poupy
active member
active member
@Egilchrist wrote:I have

2.put a test lamp across contacts ,all good even with engine running ,(possible resistance discrepancy?)

You mean that when you put a test lamp instead of the stop lamp the problem disappears? Actually, where did you connect your test lamp?

Have you tried with different powers of test lamp? Or did you try with a new stop bulb?

    

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