Unusual problem with no spark

[Willsmith]

Hello! First post here, i'll try and provide as much detail as possible.


I bought a 1987 K75S cafe racer project with most of the work already done, only issue was the LED tail light not working.


Whilst trying to find the issue I noticed a loose butt connector up by the headstock (I had taken the butt connector off for the photo).


The previous owner had cut this blue / grey wire from the ignition / head / side light loom, split it and then reconnected it.


I reconnected it using a standard connection for house wiring ( I know this isn't ideal for long term).


This fixed the tail light but when I went to start the bike, the pump whirred and it turned over but no spark.


I disconnected the wire again and it still wouldn't start. So I left the bike overnight, in the morning it started perfectly again (the wire is still disconnected).


The only answer I have managed to get from someone experienced with K bikes is that the connector that I used could have caused an unusual load on the circuit and overheated the ECU.


I have left the wire disconnected for now.


Thoughts?


Thanks in advance for your help!

[The Mighty Gryphon]

Blue/gray wire is for instrument cluster lighting.  It has some connections to other power supply wiring in the headlight and ignition switches, but other than that, I can't say why it would prevent starting unless it was used as some sort of connection to power the ignition module. 

Trying to figure out what a cafe "designer" has done to the wiring harness is one of the pastimes the owners of these bikes needs to learn to enjoy.

[Inge K.]

As you are struggling with the taillight.....the gray/blue wire is also power for the tail light,
IF that bunch of wires in the picture ends up at the RHS switch assy and the genuine ignition
switch is still in use.....and genuine wiring still is in use.....

About a LED tail light...you can't use it as is....you need to bypass the bulb monitoring relay or
add a resistor parallell With the LED.

About the missing spark.....I'll guess you just have disturbed some wires/connectors while
fiddling under the tank.

[Willsmith]

Thanks for the quick replies : )


All of the wiring is stock, ignition switch also.


Regarding the BMR ,the lights function just with the light on the dash constantly on.


The tail light was the only light not functioning but simply connecting that wire fixes it. It just temporarily stops the bike from sparking to apparently ....


I haven't touched anything below the tank just connected the blue / grey wire back up.


I probably should have mentioned I changed the battery earlier in the day to but that didn't cause any issues.


I might try and reconnect it again but with a standard butt connector and see if the problem repeats.


Thanks again for your help.