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1Back to top Go down    Tail light rewire on Thu Jun 09, 2016 11:36 am

Phil63

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Hi, I am doing a cafe racer rebuild, using a gps speedo and some basic idiot lights. One issue that is taking too much time is my tail light, it is an aftermarket light and have tested it and works well but seems wire from the "under seat" box is dead. Where is best place to run a fresh wire from? Ok if tail light is permanently on. Brake lights working fine

Thanks in advance

    

2Back to top Go down    Re: Tail light rewire on Thu Jun 09, 2016 8:42 pm

Holister

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There is a fault there that you would be better to fix rather than just a work-around.
The tail light wiring is known to short as it passes over the rear shock top mounting.
#2 fuse may be blown.
Parking lights are normally always on.

You need to put some info up about your model and year as there are some subtle differences.


__________________________________________________
1988 K100RT     VIN No.  0094680
1989 K100RT     VIN No.  0097367 (naked)  
1996 K1100RS   VIN No.  0451808
     Fuel:  95 Octane
Engine Oil: Nulon Full Synthetic 15W50
Gear Box Oil:  Nulon Synthetic 75W90
    

3Back to top Go down    Re: Tail light rewire on Fri Jun 10, 2016 7:22 am

Phil63

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Thanks Holister, sound advise. Bike is a 84 K100 RS, went over it again, am getting 14 volts at the bulb for brake lights but only 7 volts for tail light, getting 7 volts at fuse no 2 as well.
Any thoughts?
Thanks 
Phil

    

4Back to top Go down    Re: Tail light rewire on Fri Jun 10, 2016 11:31 am

Holister

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Are you taking those measurements with the bulbs removed?

Sounds like the Bulb Monitoring Unit (BMU) may be dud. It can be removed but you need to jumper some of the connections to provide continuity to the tail and brake.
The BMU is on the left side of the electrical box under the tank.


__________________________________________________
1988 K100RT     VIN No.  0094680
1989 K100RT     VIN No.  0097367 (naked)  
1996 K1100RS   VIN No.  0451808
     Fuel:  95 Octane
Engine Oil: Nulon Full Synthetic 15W50
Gear Box Oil:  Nulon Synthetic 75W90
    

5Back to top Go down    Re: Tail light rewire on Fri Jun 10, 2016 11:51 am

Phil63

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Hi Holister, my BMU looks quite different from the pic (84 K100 RS), will post pic tomorrow, looks more like one side of the instrument cluster connector, is a Bosch unit with green cover if that helps.
Ta
Phil

    

6Back to top Go down    Re: Tail light rewire on Fri Jun 10, 2016 12:34 pm

Inge K.

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@Phil63 wrote: looks more like one side of the instrument cluster connector, is a Bosch unit with green cover if that helps.

That's the turn signal relay.......BMU you find on the LHS in the relay box.


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Inge K.
K100RS -86. (first owner), K1100LTSE -94.
    

7Back to top Go down    Re: Tail light rewire on Fri Jun 10, 2016 1:58 pm

duck

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@Holister wrote:Are you taking those measurements with the bulbs removed?

Sounds like the Bulb Monitoring Unit (BMU) may be dud. It can be removed but you need to jumper some of the connections to provide continuity to the tail and brake.
The BMU is on the left side of the electrical box under the tank.

Or you can cut the guts out of the old one and make a "fake" BMU:


__________________________________________________
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    Re: Tail light rewire on Mon Jun 13, 2016 9:42 am

Phil63

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Hi guys,
Thanks for you help so far. Tried the BMU fix but to no avail, appears that I am not getting power to the BMU or the fuse box. Tail light works fine and all wiring from connector on seat rail to light is working well. I am thinking " what is the best wire to run for power to the fuse box and then on to the light, by passing the dead wire?" Unless there is something else I am missing.
Ta
Phil

    

9Back to top Go down    Re: Tail light rewire on Mon Jun 13, 2016 6:16 pm

robmack

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If you're measuring 7V on the Grey wire at Fuse#2, then you have to troubleshoot further upstream to find out where the problem lies. It could be inside the ignition switch, or inside the light switch on the right hand cluster where a poor contact is causing a voltage drop. Solve that problem before trying to work around it with an undocumented wiring kludge (which you will forget in 2 years and then have to re-learn when another problem shows up because you didn't address the first problem in the first place).


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Robert
1987 K75 @k75retro.blogspot.ca
2011 Moto Guzzi V7 Racer
http://k75retro.blogspot.ca/
    

10Back to top Go down    Re: Tail light rewire on Mon Jun 13, 2016 9:21 pm

Phil63

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Cheers, will have another crack.

    

11Back to top Go down    Re: Tail light rewire on Tue Jun 14, 2016 9:03 am

Phil63

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Hi Robmack,
Will do some further checks, taking apart the right hand switch cluster will I be met with an explosion of little springs? Will do it inside a bag.

    

12Back to top Go down    Re: Tail light rewire on Wed Jun 15, 2016 10:04 am

Holister

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I would be inclined to start with cleaning the connectors for the handlebar switch blocks with DeoxiT®. They're found under the tank, one on either side. The Trouble Shooting page off the Portal Tab has a diagram of connectors. While you're at it, clean all the other connectors you can find as well as the earth connections. You'll find them under tank and gearbox. There's an earth wire connected to the right switch block also which might be where your problem is. Corrosion on that sw.block is common.

As robmack pointed out, the ignition switch is also a problem area. There are three power circuits switched thru that switch, one being the running lights.
Ignition switch link
Once you get this out of the dash and separate the switch from the lock, you need to be careful how you open it up and where the parts fit.


__________________________________________________
1988 K100RT     VIN No.  0094680
1989 K100RT     VIN No.  0097367 (naked)  
1996 K1100RS   VIN No.  0451808
     Fuel:  95 Octane
Engine Oil: Nulon Full Synthetic 15W50
Gear Box Oil:  Nulon Synthetic 75W90
    

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