BMW K bikes (Bricks)

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1Back to top Go down   Tail light problem Empty Tail light problem on Thu Jan 24, 2019 6:04 am

AL-58

AL-58
Life time member
Life time member
Today at a rego inspection the tail light on the K100RT refused to work.

Thought it was a bulb.  The bulb looks fine and tests OK in the brake light bulb holder.

The multimeter says I have 10.7v at the tail light wires and at the terminals in the bulbholder, but when I fit the bulb it has 0 volts at the spade terminals??  The brake light which is working also shows around 10.7 so tahts not the problem itself.

Have tried a different bulb holder, a different BMU, have tried other bulbs.

I'm not strong with electrics.  If I can't beat this easily, I'll probably justbypass the BMU and take power direct to the bulb.

Any ideas?

The one last thing I can think to check is if the trailer wiring is at fault by disconnecti ng it temporarily

Al


__________________________________________________
'87 K100RS/HRD sidecar (1100 motor)  sc25 
'92 K100RS-16v (Paint it Black)

'87 K100RT with Paralever backend

"When I'm too old and too foolish to handle a sidecar I'll buy a Sportsbike"

Tail light problem K-dogs10
    

2Back to top Go down   Tail light problem Empty Re: Tail light problem on Thu Jan 24, 2019 6:25 am

Stan

Stan
Life time member
Life time member
Good thinking about the trailer connection. Many years ago when the round style of connector was in a mate had all sorts of things go wrong....blinkers blow, but random, left/right....stop light etc.. Turns out that the young son had lifted the flap of the connector and placed a one cent piece in there...for safe keeping. Rolling around shorting out pins caused major headaches and no one looked.
Good luck.


__________________________________________________
1983 K100 basic vin 0003960 colour red  GONE
1987 K100RT vin 0094685 colour, orange peel, sorry, pearl..GONE
F800R black
    

3Back to top Go down   Tail light problem Empty Re: Tail light problem on Thu Jan 24, 2019 7:44 am

charlie99

charlie99
VIP
VIP
volts but no current usually means that the connection is being made ...but just by a hairs breath of copper

is there a take off point , splice into the wiring before the bulb holder ?

is there a good earth wire ?

try measuring between the bulb holder positive ...and a good frame ground ...like back at the gearbox

or alternatively run an earth wire to the bulb holder  from the g box connection  just to prove that path is bad

once you prove the issue ...easier to solve ???



good luck Al




ooops forgot to mention  we have seen a few times that the taillight loom has been caught up behind the top rear shock mount bolt - washer , shorting , fracturing the internal cables etc ...worth a look at least


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

'86 K100 RT..#0090401 ..."Gerty" ( Gertrude Von Clickandshift ) --------O%OTail light problem Au-log10
    

4Back to top Go down   Tail light problem Empty Re: Tail light problem on Thu Jan 24, 2019 5:57 pm

AL-58

AL-58
Life time member
Life time member
The earth is a wire shared by both the tail light and the brake light.  The brake light works reliably, to me that indicates no earth problem.  Can check that just the same. 

He passed it anyway, knowing that it will get fixed Smile, made comments about throttle not returning quickly also, I think its time for a new throttle gear.


Al


__________________________________________________
'87 K100RS/HRD sidecar (1100 motor)  sc25 
'92 K100RS-16v (Paint it Black)

'87 K100RT with Paralever backend

"When I'm too old and too foolish to handle a sidecar I'll buy a Sportsbike"

Tail light problem K-dogs10
    

5Back to top Go down   Tail light problem Empty Re: Tail light problem on Thu Jan 24, 2019 7:59 pm

robmack

robmack
Life time member
Life time member
The BMU monitors the tail light, so it may be related to a problem inside the BMU and not related to any wiring fault. If when you were measuring the voltage, you did so by probing between the active terminal on the bulb and the frame earth point, then 0V could result if the driver in the BMU was faulty. Just taking a WAG here because I actually don't know how the BMU is constructed.


__________________________________________________
Robert
1987 K75 @k75retro.blogspot.ca
http://k75retro.blogspot.ca/
    

6Back to top Go down   Tail light problem Empty Re: Tail light problem on Thu Jan 24, 2019 8:02 pm

blaKey

blaKey
Life time member
Life time member
With regard to the slow throttle return...see how much gunk (old grease, dirt etcetera) is in the assembly.

I did the same and, after giving it a good clean-out (lubed it with silicone spray instead of shoving grease in there), the return action improved markedly.

(thanks Duck for the silicone tip)


__________________________________________________
Neil
K100RS 1986 RED!

Dress for the ride and the potential slide.
    

7Back to top Go down   Tail light problem Empty Re: Tail light problem on Thu Jan 24, 2019 8:32 pm

duck

duck
Life time member
Life time member
You can remove the BMU and jump the connections in the BMU connector to eliminate the BMU as the culprit.  (What I do to run LEDs.)

1) Short the front brake switch wire (Gray/Red) and the rear brake switch wire (Gray/Green) to the rear brake light wire (Gray/Yellow.)
2) Short the tail light power wire (Gray/White) to the tail light wire (Gray/Black)

Also, check Fuse #2 as that is power to the tail and parking light.

Does the tail light work when the ignition switch is in the first position? It should.  If it works in the first position but not the full on position then it could be a flaky ignition switch.


__________________________________________________
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
http://www.ClassicKBikes.com
    

8Back to top Go down   Tail light problem Empty Re: Tail light problem on Fri Jan 25, 2019 4:41 am

AL-58

AL-58
Life time member
Life time member
@robmack wrote:The BMU monitors the tail light, so it may be related to a problem inside the BMU and not related to any wiring fault.  If when you were measuring the voltage, you did so by probing between the active terminal on the bulb and the frame earth point, then 0V could result if the driver in the BMU was faulty.  Just taking a WAG here because I actually don't know how the BMU is constructed.
I've already changed BMUs with no change

Al


__________________________________________________
'87 K100RS/HRD sidecar (1100 motor)  sc25 
'92 K100RS-16v (Paint it Black)

'87 K100RT with Paralever backend

"When I'm too old and too foolish to handle a sidecar I'll buy a Sportsbike"

Tail light problem K-dogs10
    

9Back to top Go down   Tail light problem Empty Re: Tail light problem on Fri Jan 25, 2019 5:23 am

AL-58

AL-58
Life time member
Life time member
Tail light Fixed!

From an old post from Inge K:
Check if you have power at the grey/blue wire at the connector for the
ignition switch (under the tank).

Yes: the problem is in the ignition switch.
No: the problem is in the light on/off switch, or the related wiring.


I had power at the grey/blue so looked into the ignition switch side.  The switch was passing power from the red to the grey but nothing on the grey at all at the connector. It was simply a bad/dirty connection in the connector plug from the switch to the loom. Working for now but will have to get the de-oxit on it.


Al


__________________________________________________
'87 K100RS/HRD sidecar (1100 motor)  sc25 
'92 K100RS-16v (Paint it Black)

'87 K100RT with Paralever backend

"When I'm too old and too foolish to handle a sidecar I'll buy a Sportsbike"

Tail light problem K-dogs10
    

10Back to top Go down   Tail light problem Empty Re: Tail light problem on Fri Jan 25, 2019 5:53 am

charlie99

charlie99
VIP
VIP
good find Al

surely the  headlight  park lights were not working also ?

ride well mate


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

'86 K100 RT..#0090401 ..."Gerty" ( Gertrude Von Clickandshift ) --------O%OTail light problem Au-log10
    

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