I went to perform the mod listed in this page (http://www.bmwmotorcycletech.info/K-hints.htm) and when I opened mine I found I had the 2x IC system and Fleischer's information left me up short.

I have found the Data Sheets for thew ULN2455A and TC4011BP Logic sets. Has anyone done this modification to these chips or should I continue to tread this water and figure out their logic and bypass it? I really would like to be able to run different lighting and numerous extra lights rigged to my existing circuits without having the Failure Indicator Flashing at me all the time. Tips and advice is appreciated. 

On my K1100 + side car I removed the relay completely, it was a simple task when you look at the circuit to join the wires.

I have been debating that option. I would like to kinda keep the logic circuit on the for any MIL functions from the Motronic System. I will probably do that first and do some investigations into the Logic Circuits.

The Motronic unit and the BMU don't have any common functions.

Now that is some valuable information there Inge! 


Now, I am kinda confused, There are 8 groups for bulb monitoring on these IC Logic Chips. What am I missing? (I haven't spent the time to reverse engineer the wiring on it to see where all the wiring goes)

My Count on possible circuits(*Off the Top of my Head):

1. Head lamp
   
2. Rear Running Lamp
   
3. Brake Lamp
   
4. Left Turn Lamps
   
5. Right Turn Lamps
   
6. ABS Light 
   
7. Fan Light
   
8. Instrument Cluster Lamps
   
9. Coolant Temp Lamp
   
10. Fuel Level Lamp
    

The tail and brake light are the only ones monitored
.

So I am gonna crash this thread. My issue is that the tail light does not work but the brake light does. When I start the engine and apply both brakes the warning light on the dash goes out as it should however there is no power to the tail light. I have run several continuity tests as well as a complete dismantle and clean of the R/H switch block (my bike is a UK model with the light switch) and cannot find a fault however I have not worked out how to test the BMU. I did bypass the BMU by running a feed from the handle bar switch connector (positive feed) under the tank direct to the positive of the tail light. Not a good result as it seems there is negative current running through both feeds to the tail light. A right PITA to be honest. Reading threads here it seems a partial bypass of the BMU (tail light only) is possible and given the cost of these puppies it seems the logical way to go as I will still have monitoring of the brake light function. Is there anything else I should be checking first? If I pull the connector on the BMU which two wires would I bridge? The grey/black going to the tail light is easy enough but trying to work out which incoming wire to bridge to is not proving so easy.
Appreciate any help please. 
And where the %$@& is the forum search button! I can't see it for the love of looking and this subject has gotta be covered a heap of times.

KiwiK100 wrote:So I am gonna crash this thread. My issue is that the tail light does not work but the brake light does. When I start the engine and apply both brakes the warning light on the dash goes out as it should however there is no power to the tail light. I have run several continuity tests as well as a complete dismantle and clean of the R/H switch block (my bike is a UK model with the light switch) and cannot find a fault however I have not worked out how to test the BMU. I did bypass the BMU by running a feed from the handle bar switch connector (positive feed) under the tank direct to the positive of the tail light. Not a good result as it seems there is negative current running through both feeds to the tail light. A right PITA to be honest. Reading threads here it seems a partial bypass of the BMU (tail light only) is possible and given the cost of these puppies it seems the logical way to go as I will still have monitoring of the brake light function. Is there anything else I should be checking first? If I pull the connector on the BMU which two wires would I bridge? The grey/black going to the tail light is easy enough but trying to work out which incoming wire to bridge to is not proving so easy.
Appreciate any help please. 
And where the %$@& is the forum search button! I can't see it for the love of looking and this subject has gotta be covered a heap of times.

Do what I done & remove the BMU completely, have a look at the wiring diagram, it is fairly easy to do, if you can not read the wiring diagram get someone to help you.

KiwiK100 wrote: If I pull the connector on the BMU which two wires would I bridge? The grey/black going to the tail light is easy enough but trying to work out which incoming wire to bridge to is not proving so easy.

Tail light in to the BMU unit, terminal 58E, gray/white wire.
Tail light out of the BMU unit, terminal 58A, gray/black wire.

kiwi just a heads up

it is quite common that the bulb holder has become corroded in and around the actual bulb connections ...

look for "deoxit " at your nearby "jaycar store " or stockist ( also found sometimes at "pro music shops " )

its a great cleaner for anything electric ..
not saying that all the other techniques don't work ...just saying this stuff works well  and lowers the joint resistances

cheers

A blown fuse #2 will give those same symptoms. Replace the fuse and if it blows again you've got a short across the bulb to earth.
Sometimes the fuses are ok they just get a bit corroded so if its not blown try cleaning the contacts.
Always check your fuses with a meter because they can look ok.

Thanks Inge, thats what I was looking for. Glad to be aboard this forum and looking forward to the odd contribution or three. 
The manual that came with the bike is a Haynes with B&W wiring diagrams. I have a Clymer for my K12 and thats in twenty first century colour!

Charlie, the connectors at the bulb were very badly corroded and took a while to separate however they did clean up. But there is still no current reaching the bulb connector.

Kaptain, good point, as fuse #2 was blown, and blew again when I fitted a new one. This fuse is for the side stand switch (Standlicht) according to the fuse cover so I was not too concerned and did not think it was related, although as it has a clutch operated side stand lift I did wonder why there was a switch as well...

Standlicht is parklight.....if you have a 2V model you don't have a sidestand switch.

If the #2 fuse blows...then that is the reason to your problem, and not the BMU unit.
Could be a idea to check the bulb holder/Connectors/wires to the small park
light bulb above the headlight.

I'd suspect there's a short in the tail light wire as it's a bit exposed to possible damage where its cable tied to the frame r/h side under the seat.
The short could also be in the grey/white wire to the front parking light.

Kaptain and Inge, thanks very much! I will investigate over the week and report in. I have not ventured behind the fairing to access the headlight but it does appear there might not be a park light bulb in place, so some serious investigating to be done. Bugger it's cold in the garage this time of year too. -4ºC tonight...

might be an idea to check the cable run to the back lamps ...it passes the rear shock absorber top connect point
we have seen wires pinched in behind a washer and the frame right there before

good luck

Thank you Charlie, I will definitely check there too.

Yep Charlie is on the money! Exactly as suggested - trapped between the shock washer and the frame. Easily done too I reckon if you are working in poor light. 
So, if the BMU is supposedly doing its job, why is it not picking up the fault in the tail/park light? I thought the dash warning light would remain on as the BMU is designed to pick up both a defective bulb and/or a wiring fault?

good to hear

I think until the bmu unit sees input voltage to the tail lamps circuitry ....and then measures the load ,,,it wont detect a change
so if the circuit was always blowing fuses ,,,there is no input to measure the output ?...it uses a comparator circuit

does that make sense ?

cheers

Yes it does, however Haynes description of how the BMU functions states that it can detect a wire fault, but maybe not a complete failure as in a short...
Anyway, when i get it all soldered and heat shrinked we will see how it works. I'll let you know.

LOL... just goes to show you can't believe everything you read in Haynes. :suspect: "Wire fault' is a bit of a loose term. I'd say charlie nailed it with his explanation.  

JSYK the forum works better if you post your fault/question in its own thread. Makes it easier for others to find relevent info.

Glad you got it sorted.