R75/5 Ignition Switch - Mystery Wire

I own a 1976 R90/6 that I love. Fully restored it myself. However, my problem is with my father's 1971 R75/5. At the end of the summer when he went to ride it, after turning on the key smoke started pouring out of the headlight bucket. He turned it off, no flames (thank goodness), and disconnected the battery. Now, it's in my garage to fix.

So, I opened the headlight, and as you might expect, there were a lot of melted wires. Most were melted together. I documented it as best I could with photos, but it wasn't a pretty sight. It looks like the worst came from the common ground wire connecting the idiot lights; however, it also went up into the right handlebar switch.

I replaced both handlebar switches from MAXBMW (love that place!). I also had to remove the ignition and light switch (those tabs are frightening!). So, as I'm looking at the switch, things are fairly straightforward except for one mystery wire. I can't find it documented ANYWHERE; however, I've seen it in online pictures... just no mention of what it goes to... and, it's in several different color configurations. On mine it's green, but I've seen it as white and white/black.

The actual wiring diagram from the original owner's manual shows that there are no white or white/black wires attaching to the ignition and light switch. Also, the only green wires I see illustrated all come from post 15, and include the common ground for the idiot lights (to flasher relay post 31), one going to the right ignition coil, and one going to the horn (post 15). Yet, I have this unidentified green wire, soldered to the switch, which is energized when the key is in the on position. It's looking kind of ragged, and I'll replace it... just need to know where the other end goes! Haha.

And, yes, I am labelling every wire with shrink wrap. I find that makes my life much easier down the road.

I've attached 2 pics showing both sides of the switch. In both pics I have circled the connection spot in green and used an arrow to point to the wire. Any help would be greatly appreciated!!

Also, if there's any interest, I've got a spreadsheet (saved as a .pdf) that shows every wire and where it goes on this R75/5, including color and size. I'll gladly share it, if told where you'd like me to post it.

Not sure where you'll see the responses first, so I'll repost what I did on the VBMWMO forum.

I've looked in my Haynes and the 30/51 post on the ignition switch board shows two wires attached to it. One solid red, fairly thick, going to terminal 30 on the starter relay. Another green wire with red stripes goes to terminal 30 on the lights/horn switch. As I recall, red wires are hot all the time, while green wires with red stripes are switched power.

Do you have anything currently going to that terminal on the horn switch? Maybe someone replaced the original green/red wire with solid green at some point.

That's my take.

20774 said:

Not sure where you'll see the responses first, so I'll repost what I did on the VBMWMO forum.

I've looked in my Haynes and the 30/51 post on the ignition switch board shows two wires attached to it. One solid red, fairly thick, going to terminal 30 on the starter relay. Another green wire with red stripes goes to terminal 30 on the lights/horn switch. As I recall, red wires are hot all the time, while green wires with red stripes are switched power.

Do you have anything currently going to that terminal on the horn switch? Maybe someone replaced the original green/red wire with solid green at some point.

That's my take.

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Appreciate the input. This wire is not attached to the terminal. It is soldered to the actual switch board... near the terminal.

OK, I missed that. I've never been inside these things, although I have them on my vintage bikes. Obviously, you're sticking in the nail-key and twisting around to engine the lights and also to provide power to the ignition system. I'm thinking that the arc on the left in the top picture is the ground plane while the arc on the right are the various positions of the ignition - off, lights, ignition on. That suggests to me that the right hand arc has to have power to it and thus the green wire is associated with power. You say this is an early /5...these didn't come fused. Is it possible that this green wire might have been connected to some add-on fuses somewhere else in the circuit?

20774 said:

OK, I missed that. I've never been inside these things, although I have them on my vintage bikes. Obviously, you're sticking in the nail-key and twisting around to engine the lights and also to provide power to the ignition system. I'm thinking that the arc on the left in the top picture is the ground plane while the arc on the right are the various positions of the ignition - off, lights, ignition on. That suggests to me that the right hand arc has to have power to it and thus the green wire is associated with power. You say this is an early /5...these didn't come fused. Is it possible that this green wire might have been connected to some add-on fuses somewhere else in the circuit?

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This is a 1971 R75/5. You're correct, there are no fuses. I know what everything else on the board does... just need to know where the green wire attaches. However, I do sincerely appreciate your assistance.

green wire

IF your switch has not been tampered with:
The green wire is switched to hot with the ignition switch turned on. It doesn't matter if the lighting (headlight or parking light) is on or not. On a non fused system the green wire powers the idiot lights, the ignition, the brake light switches, the turn signal relay and the horn.
On a fused system the green wire goes to a fuse. Green/black wires go from the fuse.
There are plenty of sources for wiring diagrams to be found on the internet! Get one before you smoke-check any more wiring harnesses.

1074 said:

IF your switch has not been tampered with:
The green wire is switched to hot with the ignition switch turned on. It doesn't matter if the lighting (headlight or parking light) is on or not. On a non fused system the green wire powers the idiot lights, the ignition, the brake light switches, the turn signal relay and the horn.
On a fused system the green wire goes to a fuse. Green/black wires go from the fuse.
There are plenty of sources for wiring diagrams to be found on the internet! Get one before you smoke-check any more wiring harnesses.

Click to expand...

I didn't "smoke check" anything. The bike was purchased and running. My father started it one day, and it was smoking. I opened the headlight and found a mess of melted wires. I've checked EVERY source for wiring diagrams and this wire is NOT listed on any of them. I have the actual wiring diagram from the owner's manual for this bike... and it's not there either. However, it does appear in several pictures I've found on the internet. Kind of as I explained. In fact, in the pictures I've found this wire tends to be either white or white/black. However, on mine it is green.

I'm asking for help...

1) You will be adding fuses to the repair, correct?
2) Can you share how/where you produced the heat shrink labels?

ebeeby said:

1) You will be adding fuses to the repair, correct?
2) Can you share how/where you produced the heat shrink labels?

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Yes, I will be adding fuses... after I figure out where that one wire goes. The labels were made using a DYMO label maker with their shrink wrap, which comes in several sizes. You can find it on Amazon. Well worth it if you're doing any labelling. I have the DYMO Rhino Industrial 5200.

Confused

Drbillk said:

I didn't "smoke check" anything. The bike was purchased and running. My father started it one day, and it was smoking. I opened the headlight and found a mess of melted wires. I've checked EVERY source for wiring diagrams and this wire is NOT listed on any of them. I have the actual wiring diagram from the owner's manual for this bike... and it's not there either. However, it does appear in several pictures I've found on the internet. Kind of as I explained. In fact, in the pictures I've found this wire tends to be either white or white/black. However, on mine it is green.

I'm asking for help...

View attachment 59672

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I apologize for not being clear enough. I'm thankful that I never had to write a textbook.
Sorry. "smoke check" is a term used when something goes wrong and the wires get hot enough to melt the insulation to the point of burning thus producing smoke. I did not mean to imply that you, yourself caused the wiring to heat up and melt the insulation.
Also sorry that I did not provide the help that you asked for.
I did NOT tell you that there is NO common ground wire for the idiot lights. There is a common hot wire that goes to the idiot lights and provides power to the turn signal relay (flasher). It should be green.
I did NOT tell you that I have never seen a black with white wire on a stock /5. I have seen this colored wire on /2 models.
I did NOT tell you that a white wire goes from the /5 high-low beam switch to the high beam headlight bulb.
And of course, I did NOT tell you how to duplicate the fused wiring system found on the later /5 models.
You might want to get with the Yahoo Slash 5 United group where a lot of repair information for /5s is located. Just remember that all questions answered are from people with a wide variety of knowledge and some of it is not exactly correct.

I just saw this. If you still have not figured out what that wire is, I can crack open both of my /5's and tell you exactly what it hooks up to.. let me know, Dave

Thanks

googledave said:

I just saw this. If you still have not figured out what that wire is, I can crack open both of my /5's and tell you exactly what it hooks up to.. let me know, Dave

Click to expand...

Mystery solved... The white goes nowhere. Thanks for the offer