Electrical Question - Stumped

[the_unknown]

So I have an issue that I can't seem to get my head around and I'm hoping the guru's here can help solve.

Long story short, A buddy and I have built a k100 that has a GSXR 750 front end and hand controls. We have an Acewell MD085 gauge and the BEP 3.0

As it stands now, everything functions properly except for the horn. I have fuel level, speed, rpms, even coolant temp with the acewell 10m x 1 plug in the coolant drain plug line. The bike is road worthy and we've done some testing on it  but the horn issue is one of the last things we need to track down.

So here is the rub. With the key in the ON position and the kill switch off, the horn relay will fire when the button is pressed. As soon as we turn off the kill switch to start the bike, the horn no longer will function by pressing the button.

Another "interesting" thing is that with the kill switch on (bike can't start) the gauge isn't illuminated. As we turn it on, the Acewell gauge lights up. With the kill switch on (bike can't start) and the pressing the horn button, the Acewell gauge will light up until i let go of the horn button.

I've studied the wiring diagram and triple checked connections, jumpered connections, and can't seem to figure this out. Any ideas?

[daveson]

Cast an optic nerve over the power to the kill switch. The wire should be green, not green/blue. The blue stripe is sometimes hard to see with the aged wiring we have (and the aged eyes some of us have)

Power to the headlight switch should be green/blue.

[the_unknown]

Thanks for the tip. I bypassed the switch with the 9 prong plug and a jumper. Same results unfortunately. This is such a weird issue, I'm leaning towards the load shedding relay but I have swapped them and they both seem to work otherwise.

Another thing of note that may help is that none of the kill switches are functioning. Nuetral switch and Clutch switch don't have any effect on starting.

[Scott_]

What year of K100 are you working with.... I can send you a copy of the official BMW schematics if you would like.

The horn relay gets power from the load shed relay, and the LSR is activated with the ignition switch. The stock kill switch has no effect on the LSR or the horn relay.
The stock horn switch simply connects the horn relay coil (-) lead(brown/yellow term85) to ground(brown).
In the LH multi-function switch connector terminal #9 should be the brown/yellow lead(1 wire .5mm) for the horn relay and terminal #6(2 brown wires, .5mm and .75mm) should be the ground leads.
The .5mm brown wire goes to the RH multi-function switch, and the .75mm brown wire goes to the frame ground connection.

It sounds like your controls may not have the same function as the oem bmw.

As far as the kill switch wires.
Terminal #9(input), 1mm green, power in from ignition switch terminal 15. Also a .5mm green wire goes to LSR coil term 86.
Terminal #2(output),(3 wires) (1) .5mm green/yellow out to ignition controller term 10. (1) 1mm green/yellow out to spark plug coils + lead. (1) 1mm green/yellow out to fuse #1 and to FI relay term 86.

[the_unknown]

Scott, Thanks for the reply. It's a 87 K100 LT.

I have been using the schematics from here:
http://www.kbikeparts.com/classickbikes.com/ckb.tech/0.ckb.tech.files/kwiring/Early%20K75%20K100/K100_Early_Wiring_Diagram.jpeg

This brown 0.5mm wire that goes to the RH switch is just a ground correct? The stock GSXR switches didn't need a ground on that side so we don't have one.

It's so weird that everything works except for the horn. But turn that kill switch off and the horn then works. I have the switches for the starter and the kill switch wired up properly as the bike starts up just fine.

[the_unknown]

Here is a video of it. You can hear the horn relay firing (I disconnected the horn after my ears started bleeding from hitting it so often) with the kill switch off and then not fire with it ready to start.

[Scott_]

There were a few changes from '85(the 1st drawings I was looking at) to '87LT that you have, but only how multiple wires terminated, colors and locations still are the same for what you're dealing with.

What I see, and hear, there is obviously something not wired correctly.

How have you addressed your turn signal triggers. The bmw signal relay uses a switched ground to trigger the signals and the signal cancel function(why the brown wire to the RH switch plug).

I'll try and attach what I have so you can compare to Drakes.

[daveson]

Maybe a GSXR doesn't need earth on the right hand side, but a brick does. Maybe that's why the gauge doesn't light until you press the horn, then it steals earth from the horn.

[the_unknown]

Maybe a GSXR doesn't need earth on the right hand side, but a brick does. Maybe that's why the cluster doesn't light until you press the horn, then it steals earth from the horn.

The earth on the right side is only used for the turn signal and turn signal cancel switch as far as I can tell. All turn signal functions are on the left side for a GSXR. I grounded that wire as a test anyways and it changed nothing.

[the_unknown]

There were a few changes from '85(the 1st drawings I was looking at) to '87LT that you have, but only how multiple wires terminated, colors and locations still are the same for what you're dealing with.

What I see, and hear, there is obviously something not wired correctly.

How have you addressed your turn signal triggers. The bmw signal relay uses a switched ground to trigger the signals and the signal cancel function(why the brown wire to the RH switch plug).

I'll try and attach what I have so you can compare to Drakes.

Thanks for the pdf. I am looking at it now but it's a little tougher to read than the one I posted 

I moved all flasher functionality over to the left controls for the GSXR. Everything functions as it should, I can send a video over for proof if that would help. I clipped the 7 prong inside the flasher unit to get the LEDs to flash.

[daveson]

If an earth jumper wire to the gauge lights it up, I'd take it as a sign of an earth failure to the gauge. 

By the way which prongs were bridged with the jumper wire to the nine prong plug?

[the_unknown]

If an earth jumper wire to the cluster lights it up, I'd take it as a sign of an earth failure to the cluster.

By the way which prongs were bridged with the jumper wire to the nine prong plug?

On the harness side looking at the plug with the 3 rounded potions at the top
top row :-green/yellow traced wire in middle
bottom row: green wire on right side.

A question for stock k100 riders. I didn't really ride this thing enough before we cafe'ed it so I can't remember but does the kill switch also turn off everything (except for the clock, obviously) to the gauges as well?

[the_unknown]

Figured it out! I tested the brown/yellow wire for the horn and grounded it directly to the frame. It activated the horn relay whether or not the kill switch was on. So it turns out that the clutch switch for the GSXR shares a ground with the horn switch. On the bricks, the clutch switch is completely separate from the horn switch. When we initially wired it, we made the bad assumption that the ground would work for both. Since the clutch kill switch doesn't work anyways, i removed the wire and connected it directly to ground. Voila, horn works! Thanks for your help, it actually got me thinking about narrowing down the connections one by one to isolate everything.

[the_unknown]

I guess i should at least update with some pics of her.
This is how we bought her. Got her for 800 bucks off of CL years ago.

Life happened and we neglected her for a while but this last summer we got it nearly to 100%
Here she is as of last week.

[rbm]

Try this schematic off my Google Drive.  https://drive.google.com/file/d/0B3UPbNZRyr1rWHlMbC01eGtwR1U/view?usp=sharing

What wiring modifications did you make during construction to adapt the Japanese controls to the BMW electrics?  If the horn is your only problem, then install an auxillary fuse box and wire the horn circuit through that.

[the_unknown]

Thanks for that document rbm, that is a much easier to read schematic than what I had been using earlier with the link/pic I posted up above.