duck wrote:You can cure this by getting rid of the BMU.  The BMU is the black box on the left side of the relay box right in front of the fuses.  Once you've removed it, short the following wires in the BMU socket:

Short the front brake switch wire(Gray/Red) and the rear brake switch wire(Gray/Green) to the rear brake light(Gray/Yellow.)

Short the tail light power(gray/white) to the tail light wire(Gray/Black)

kioolt wrote:By you saying you are converting it to a café racer I'm getting that you have done some rewiring in addition to the led bulb.  If memory serves me correctly the original tail and brake light were separate bulbs.  When you installed the led bulb did you use one that is a single unit?  Did you remember to hook up the brown ground wire?

kioolt wrote:Can you post the wiring diagram you used and also the information on the bulb you are using?  I may be able to help.

1. How do you know the fuse is good? They can look ok but are dud. Put a meter on it to be sure.
   
2. Do you have power to the fuse holder? Fuse #2 is fed direct from the ignition sw. on the grey wire. Front park and tail light are the only things on that circuit. Test = DMM @20Vdc range, fuse +terminal to earth, ignition/park sw on.
   
3. Do you have continuity from fuse #2 to the tail light? Remove the bulb
   
4. Is there an earth short on that circuit? Remove the bulb
   
5. Do both LEDs bench test ok?
   

• the fuse or fuse holder is dud,
  
• the ignition sw is not connecting that circuit,
  
• you've got a short or
  
• the BMU is faulty
  

Mumbles wrote:I put my volt meter on the #2 fuse and got 11.8 volts so the fuse (depends which side you measured from) and fuse box is ok. I then put the meter on the tail light connection and got 6.75 volts? I put it on the brake light connection and it had 11.8 volts.

What does the 6.75 volts mean on the tail light connection?
That voltage is a bit strange. Did you take the LED out?

It's a led tail and brake light combination.

Mumbles wrote:Your jumpers match what I did. I did not remove the led. I thought the voltage was strange also. 
You need to remove the LED or disconnect the connector to properly measure the tail voltage. Follow robmack's instructions.
Seeing as the voltage was measured with the bulb in place what you have measured is the voltage drop across the LED.
LEDs can be dimmed with a resistor and I suspect that's how this single LED tail/stop works which confirms the use of a drop resistor in the light fitting on the tail light circuit and why you're getting 6.75V.
I'm starting to think the LED itself may be faulty.

I took off the the original head light, turn signals, tail light and instrument cluster. I put on led turn signals front and back and they work fine. Head light works fine also. I put a digital speedo (Vipor) on it. So far everything works that I want to work except that tail light.

The wire for the old head light parking light is just hanging. I measured the voltage rom the outside of the fuse. That tells you there's power to the fuse holder only depending on which side of the fuse you measured from. The only definative test for a fuse is to take it out and check continuity across the spades. However, you have a voltage at the tail so I'd say the fuse is intact.

1. From the right side of the #2 fuse holder (see 2 tiny square holes just above the fuse) to the tail light connector. A good reading will be around 0.5Ω, otherwise...
   - I'm assuming you soldered the jumper wires?? Could be a dry solder. Measure accross the outside pins.
   - That just leaves the fuse. You need to measure the resistance on that to be sure. It could more likely be corroded fuse/holder contacts. This is a known problem with other issues. With the fuse inplace, stick your DMM probes into the 2 tiny square holes just above the fuse. You should get less than 0.5Ω
   
   
2. If that checks out OK... with the fuse-to-tail wire still isolated, measure the resistance from the tail light connector to the negative terminal on the battery. That will tell you if the tail light wire is shorting to earth. A good reading will be infinity. Robmack already detailed this test, but running the park light wire to the rear as you did, does not conclusively rule out an earth short.
   
   
3. If that checks out OK... with the brake off, measure the resistance from the tail light connector to the brake light connector. That will tell you if the wire is shorting to the brake light wire. They are cabled together from the BMU back along the R/H side of the frame just below the seat. A critical point is where it passes by the rear shockie bolt.
   

Kaptain Holister wrote:Correct... both tests indicate something amiss upstream. 6V is indicating there's a resistance somewhere from the fuse (11.8V) to the tail connector (6V). There may be a short involved but not necessarily.

With the BMU/jumper in place, ignition sw completely off, fuse #2 inplace, LED removed, set DMM to ohms scale and measure...

1. From the right side of the #2 fuse holder (see 2 tiny square holes just above the fuse) to the tail light connector. A good reading will be around 0.5Ω, otherwise...I get 0.0
   - I'm assuming you soldered the jumper wires?? Yes Could be a dry solder. Measure accross the outside pins. I get 0.0 there also.
   - That just leaves the fuse. You need to measure the resistance on that to be sure. It could more likely be corroded fuse/holder contacts.The contacts and fuse look brand new. Bike only has 3,000 miles on it.  This is a known problem with other issues. With the fuse inplace, stick your DMM probes into the 2 tiny square holes just above the fuse. You should get less than 0.5Ω  I get 0.0 there as well. The lowest ohms setting on my volt meter 20 and starts with a 1. then when I make the connect it starts about 3 and goes down to o.
   
   
2. If that checks out OK... with the fuse-to-tail wire still isolated, measure the resistance from the tail light connector to the negative terminal on the battery. The meter doesn't even change when I did this on either the black or red tail light wires or the wiring harness gray/yellow or gray/black. That will tell you if the tail light wire is shorting to earth. A good reading will be infinity. Robmack already detailed this test, but running the park light wire to the rear as you did, does not conclusively rule out an earth short.
   
   
3. If that checks out OK... with the brake off, measure the resistance from the tail light connector to the brake light connector. The meter doesn't change on either wires here either. That will tell you if the wire is shorting to the brake light wire. They are cabled together from the BMU back along the R/H side of the frame just below the seat. A critical point is where it passes by the rear shockie bolt.
   

Have you bench tested the LED? I did and neither brake or tail light would eliminate. I put it back on the wiring harness and it will light only half the LEDs if both the white and red wires are hooked up. Would be good to know that the tail light does actually light up when 12V is applied. I can't read anywhere where you mention this. Easy way to do this is to connect the earth connector to the white wire and run a test lead from the +battery and apply to the red and black wire one at a time.