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Discussion Starter · #1 ·
Good morning all,

I acquired a 2007' 1200LT that the former owner tipped over (front brake locked up apparently) and ran into the back of a car, damaging the front end, which was pushed toward the rear of the bike. I disassembled the entire front end, replaced the frame, and repaired or replaced anything I could find that was damaged. I have the bike back together, and cleaned up. As I fitted a new battery, the bike started right up, and runs great. Everything works, except the speedo, the hydroelectric center stand, and the ABS lights are flashing (4 per second, with solid warning light). As I've investigated closer, it appears a former owner electrically bypassed the ABS unit with two relays and some shoddy wiring. When I first started the bike, the servo pump ran continuously, and had the typical excellent brake power. I believe the ABS pump must have failed previously, and the owner bypassed it, with no speedometer fix, as the bike only shows 28k miles on it. When I put the new battery in, there were two ground wires twisted together in the mess of wiring connected to the ABS wiring, which were connected to the negative post of the battery, so I reconnected them like it had been done previously, and the brakes worked as just described. I decided to put a circle connector on the end of those ground wires and reconnect it, now the servo pump is off, and the braking power is lost (although still ridable). I will check for a fuse, or some other loss of connection later today, but I have a few questions. By the way, I got the bike for the price of two new tires which were included with the bike, so it was free to me, and I don't mind spending a little money on it;

1) Does the ABS system have to be working correctly, and not bypassed to have the speedometer work?

2) Is there a wiring diagram that correctly shows how to properly bypass the ABS system on this year of bike? (I have searched endlessly and cannot find one, although I have bypassed other BMW motorcycles without a single problem from internet searches)

3) Is the ABS unit, and the servo pump all part of the same unit? In other words, if I were to reverse the wiring work, and try to put it all back to stock, and have the ABS unit rebuilt, would that likely fix the speedo not working, and make the servo pump only come on when the brakes are applied?

Thank you all in advance, this is a new model for me, so I'm just working through the kinks.....
 

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2005 K1200LT
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First off in a fully functioning LT the ABS uses the signal from the rear wheel sensor to generate two speed related signals (TA- and TAS). Both of these are sent to the dash and drive the speedometer and odometer. The dash then generates a signal (TAA) from these two input signals and sends that to the cruise control, EHCS controller and the turn signal flasher.

Most often when the servo system fails, the hydraulics are bypassed, while the electronics are retained to generate those signals. So for proper bypass nothing is done to the electronics other than a relay removal and the snipping of one wire both of which are done to stop the flashing warning lights. If the servos were running often they just pull the internal connectors to the servo motors. Hydraulically bypassed the brake will work just fine but just no ABS function.

Pin 9 (brown/red) wire is the one that gets cut for one light and the other is driven from a normally closed relay driven from pin 10 (brown/yellow). Cutting this wire will not stop the light from illuminating as the relay is normally closed and the switched power goes through it to illuminate the light , thus relay removal OR cut the wire on pin 10 and ground the bike side of the cut wire to extinguish the light.

Barring all the above, you undo those and repair the unit it will return the speedo and related functions to the bike.
 
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Discussion Starter · #3 ·
First off in a fully functioning LT the ABS uses the signal from the rear wheel sensor to generate two speed related signals (TA- and TAS). Both of these are sent to the dash and drive the speedometer and odometer. The dash then generates a signal (TAA) from these two input signals and sends that to the cruise control, EHCS controller and the turn signal flasher.

Most often when the servo system fails, the hydraulics are bypassed, while the electronics are retained to generate those signals. So for proper bypass nothing is done to the electronics other than a relay removal and the snipping of one wire both of which are done to stop the flashing warning lights. If the servos were running often they just pull the internal connectors to the servo motors. Hydraulically bypassed the brake will work just fine but just no ABS function.

Pin 9 (brown/red) wire is the one that gets cut for one light and the other is driven from a normally closed relay driven from pin 10 (brown/yellow). Cutting this wire will not stop the light from illuminating as the relay is normally closed and the switched power goes through it to illuminate the light , thus relay removal OR cut the wire on pin 10 and ground the bike side of the cut wire to extinguish the light.

Barring all the above, you undo those and repair the unit it will return the speedo and related functions to the bike.
This is excellent help, thank you John. I will digest this, and take a closer look at what I need to do to remove the other miscellaneous wiring that is there, and make the above changes first, and see where we're at. I did notice, that the front ABS/wheel speed sensor was not plugged in, and for the life of me, couldn't find a suitable plug under that front fairing to plug it into. I finally found a plug that fit correctly, which was close to the left horn plug, but some previous owner had some kind of dead end plug over it, as if to keep the water out. I can't find any other plug that fits the ABS sensor plug end, except for that one. Does that sound like the right place to find the connector on the bike harness to plug that front ABS sensor into? Thanks again for your help, I really appreciate it!
 

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Yup you got it right.

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Discussion Starter · #5 ·
Goodness, I knew there was a place to attach the plug on that frame support bar, however, I couldn't find a plug in that part of the harness to connect the ABS sensor to. I will have to take the plastics back off and dig around....I have a wiring diagram for the bike in my manual, so I'll try again to match this plug up.....Thanks again.
 

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2005 K1200LT
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Should be a shielded wire pair with Yellow/Red and Yellow/Brown
 
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On the 'bike I sorted, the PO had connected the ABS front sensor plug to the horn socket that took some finding, but of course the colour codes and lack of screening gave it away.
 

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Discussion Starter · #8 ·
On the 'bike I sorted, the PO had connected the ABS front sensor plug to the horn socket that took some finding, but of course the colour codes and lack of screening gave it away.
Interesting..... There's already like two horn plugs already on that side on my bike, and their orientation doesn't fit my ABS plug, thankfully....
 

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Discussion Starter · #9 ·
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So, this plug, obviously not the correct plug, fits the ABS sensor.... If Im not mistaken, this should be a horn plug? (Im color blind.......lol) Ill dig deeper this afternoon, but that looks like a ground (brown), and a grey/blue?? This is the bike wiring harness side.....
 

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View attachment 175525

So, this plug, obviously not the correct plug, fits the ABS sensor.... If Im not mistaken, this should be a horn plug? (Im color blind.......lol) Ill dig deeper this afternoon, but that looks like a ground (brown), and a grey/blue?? This is the bike wiring harness side.....
I would say brown and green/blue or maybe green/gray, but the picture looks more blue to me. I am not colorblind, but often pictures are not totally accurate in color reproduction and this looks like a grayish blue, but I would call it blue as a first choice. Also, the wire looks like it has been pinched pretty hard right near where you are holding it.
 

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It is a green / blue and is for the horn. The one you are looking for may be connected to the horn. It has a screened cable to it.
 

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Discussion Starter · #12 ·
It is a green / blue and is for the horn. The one you are looking for may be connected to the horn. It has a screened cable to it.
It looks like I've done the same thing that happened to your bike...lol.... Now I'm wondering how the heck the horn worked when I tested the button... lol... I'll get this fixed this afternoon, and get back with whatever color cables I've connected to the horn....
 

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Discussion Starter · #13 ·
Ive also figured out why the brake servos were on all the time once the key was turned on.... somebody cut and twisted the two rear brake switch wires together.......on the harness side.....

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It looks like I've done the same thing that happened to your bike...lol.... Now I'm wondering how the heck the horn worked when I tested the button... lol... I'll get this fixed this afternoon, and get back with whatever color cables I've connected to the horn....
Because there are twin horns!
 

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2005 K1200LT
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Horn wire colors are Green/Gray on the 05 at least. Yeah the brake switches are normally closed and open for activation on the iABS version, just the opposite on the ABS II on the early bikes. You have a real bag of worms there.
 

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Discussion Starter · #17 ·
Because there are twin horns!
Isnt there supposed to be a horn on each side of the bike? There are two connectors on the left, both of which work to operate the horn (tested independently), and one plug on the right..... the plug on the right appears to have a brown ground, and a white (or grey) with a black stripe......
Because there are twin horns!
Ok, I thought there should be one horne on each side of the bike according to the illustration in the manual (one left lead wouldnt reach to the right horn) however, as I lool at my pictures taking it apart, there are two horns on the left side, as you mentioned... and both now work....
 

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Both horns are right next to each other.

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