Can you help me figure out what's wrong?

[zombiepotatosalad]

A quick look shows me one possible spot for your trouble. From left to right you have a bundle of wires in a taped bundle. This is not factory. Can you trace the bundle back outside the shell to the right controls? I don't know what the previous owner did but I guess the black wire (I don't have my schematic handy so I am relying on memory) is possibly the kill switch wire. Regardless, wires from the factory if they have ninety degree plug ends on them inside the headlight shell will plug onto the same color terminal on the circuit board. I see a white (what looks like a factory plug) plugged into a black crimped on connector with tape over it. Same with a yellow wire going to green.

If you get my drift, this is not correct. Do you have a wiring diagram for the bike, at this point you will need one to figure out what the previous owner was trying to accomplish.

I always stress keeping stock wiring stock, and in a case like this if possible reverting back to stock.

If I get out to my shop tomorrow, I will try to see if I can find what goes where.

All the terminals plugging into the circuit board should be the same color wire as the circuit board. Maybe the previous owner replaced the stock right hand switch control with one that had a shorter wire bundle and added a non correct color group of wires to bridge the length distance. If so, he may well have mis wired somewhere.

Good luck and good hunting. St.

The black wire runs into a gray wire which goes into what appears to be a gray colored area on the board.

[STEVENRANKIN]

OKAY, I have my wiring diagram for a 77S.

From right control kill switch, Green wire goes to what looks like terminal 15 on circuit board, left side of the fuse. There is another green wire at that pin on the same side that goes directly to the ignition switch.

Also on the kill switch is a green blue wire going direct to the coil.

Solid gray wires connect to the left side of the fuse terminal 58, there are three wires, one goes to terminal 87b on the headlight relay. One goes two the ignition switch. The last gray wire goes to the left headlight switch on the left handlebar control.

Black wires are only found on the coils themselves.

Starter button is a blue /yellow wire and brown/yellow. Tun signal is green/yellow @ 49a, for left, a blue/red wire, right is blue/black.

Hope this helps, good luck, St.

[zombiepotatosalad]

A quick look shows me one possible spot for your trouble. From left to right you have a bundle of wires in a taped bundle. This is not factory. Can you trace the bundle back outside the shell to the right controls? I don't know what the previous owner did but I guess the black wire (I don't have my schematic handy so I am relying on memory) is possibly the kill switch wire. Regardless, wires from the factory if they have ninety degree plug ends on them inside the headlight shell will plug onto the same color terminal on the circuit board. I see a white (what looks like a factory plug) plugged into a black crimped on connector with tape over it. Same with a yellow wire going to green.

If you get my drift, this is not correct. Do you have a wiring diagram for the bike, at this point you will need one to figure out what the previous owner was trying to accomplish.

I always stress keeping stock wiring stock, and in a case like this if possible reverting back to stock.

If I get out to my shop tomorrow, I will try to see if I can find what goes where.

All the terminals plugging into the circuit board should be the same color wire as the circuit board. Maybe the previous owner replaced the stock right hand switch control with one that had a shorter wire bundle and added a non correct color group of wires to bridge the length distance. If so, he may well have mis wired somewhere.

Good luck and good hunting. St.

OKAY, I have my wiring diagram for a 77S.

From right control kill switch, Green wire goes to what looks like terminal 15 on circuit board, left side of the fuse. There is another green wire at that pin on the same side that goes directly to the ignition switch.

Also on the kill switch is a green blue wire going direct to the coil.

Solid gray wires connect to the left side of the fuse terminal 58, there are three wires, one goes to terminal 87b on the headlight relay. One goes two the ignition switch. The last gray wire goes to the left headlight switch on the left handlebar control.

Black wires are only found on the coils themselves.

Starter button is a blue /yellow wire and brown/yellow. Tun signal is green/yellow @ 49a, for left, a blue/red wire, right is blue/black.

Hope this helps, good luck, St.

Followed the light green wire from the kill switch to the bucket, found this. I could have pointed to the wrong wire in the picture, though, I'm working with a phone flashlight in the dark. I'll have to check it again in the daylight. 20221128_204059.jpg20221128_205023.jpg

[Guenther]

zombiepotatosalad, where's home? Maybe there is someone in your neighborhood who can help.

[zombiepotatosalad]

zombiepotatosalad, where's home? Maybe there is someone in your neighborhood who can help.

Davenport, Iowa. I don't think there's anyone really close who'd also want to work in the cold (I don't have a garage, so I do all the work in the backyard).

[STEVENRANKIN]

Well, you are a bit too far from me for me to show up to help, sorry. Cold doesn't bother me, hot does, LOL.

At the switch itself and where the bundle of wires enters into the headlight shell, those wires are color coded and should terminate on the circuit board. The green wire is a pain if I recall, it can have a junction somewhere inside that is not terminated on the board. Two of the green wires are.

Sorry, the photo didn't help much. Have you traces the green wire from the right switch and the ignition switch to terminal 15? Don't pay any attention to the scoctch lock crimp just confirm those two wires go there for now.

I will take another gander later today after I sort out a problem with my car at the dealership. Have you found a wiring schematic yet? I suggest the ones EME sells. In my case for now, I am working out of the latest version of the Haynes repair manual. I don't have an EME diagram on hand for the 77S, only for a 78.

Take a look in the MOA anonymous book (online or book) and see if perhaps there is a club member close by who might help, it is a long shot but hey, if you don't ask, or check, you will never know. It is too bad it is winter now and I am recovering from my accident and can't take a trip out to help. It has been a long time since I was in Iowa to visit my sister when she lived there. St.

[179212]

Possibly contact the the Iowa Air Marshel, Tina might know someone who could be helpful.

[STEVENRANKIN]

Looking at the diagram agin I see a green wire connected to the right side of the fuse on the board at 15. This goes from there to the turn signal relay pin 49.
There is another green wire from the ignition switch 56 to the headlight switch in the left handlebar control.

At this point I can't help much more, you need to determine why the green wires in your picture are connected in the manner they are.

I suggest putting them back if possible onto the correct terminals

When you get a wiring diagram, I will be happy to see if I can help further. Attaching a diagram to the form may be possible but my taking a picture shrinking it to proper size kind of gives a hard to read sclkhematic.

Take a look at this guy's site, maybe he has a link or https://brook.reams.me/bmw-motorcycl...al-components/ that will help for now.

Good luck St,

[zombiepotatosalad]

Found something. The kill switch wire runs to the black 90 degree plug. However, the blue crimper thing holds another green wire which runs to one of the plugs in the green area. Why was it doubled? The 90 degree connector was plugged in to this greenish wire with a spade connector.

I don't know why it uploads my pictures sideways.

1669753091576423697874241220575.jpg
16697531934487143880952773715216.jpg
16697533265354593908828150989409.jpg

[zombiepotatosalad]

Here's a black wire that was unplugged, it shares a harness with an orange wire (that's blue crimper thing crimped to a blue wire with a red stripe), and a gray wire.

Also, this board doesn't have fuses in the regular places.
20221129_142913.jpg

[STEVENRANKIN]

Yes, I saw your PO had wired two fuses and their holders in a non BMW way. I forgot to say, check those fuses to see if they are good? It really doesn't matter the fuses are not 100% original, look to see they are wired same as the original fuses were, the hot side on one side and the protected side on the other.

I have no idea why the PO did what he did or where those wires go now and that most likely is part of your problem.

On your second picture I see one of the green wires plugged into a spot on the board in the wrong place and with the wrong kind of terminal end. I have marked it with red lines.

The terminal with the blue scotch lock crimp near your thumb should be plugged into the green section of the circuit board. That style insulated connector is a key tell tale of things plugged into the board, that is the type of factory connector. I marked the picture with an arrow where I think that plug should go. I can't help you much else.

Examine the bundles of wires entering into the headlight shell, factory done wiring is neat, tidy with proper connections similar to the one I pointed out. Any bundle of wire that is wrapped in electrical tape as is one I see and any wire with non stock connectors or crimp on dime store terminals is suspect. Trace things back to the source. Make sure things are plugged into the board in the proper colored spots. It is a jumping bundle of snakes working inside the headlight, not one of my favorite things to do, but you will have to dig into the non stock stuff, figure out what the intention was and in my best advice, put things back to stock or as close as you can. Before going any further, wait until you get your wiring schematic. Yes, things are color coded such but you really need a wiring diagram to figure out how things are wired and work. Good luck. St.

16697531934487143880952773715216-2.pdf1669753091576423697874241220575.jpg16697531934487143880952773715216.jpg

[STEVENRANKIN]

One picture did not attach.

16697531934487143880952773715216-2.jpg

[Guenther]

Maybe a 'talk' with the previous owner would help to know the reason for all these modifications.

Can someone post a picture of his R100S?

My diagram does not match the colors of some wires which I see in the pictures.

[zombiepotatosalad]

[QUOTE=STEVENRANKIN;1292541]One picture did not attach.

What should I do with the doubled-back green wire? I think there should be two things plugged into the green area on the board, and the kill switch wire you indicated is one of them. So the other one plugged into the green area should be unplugged, as it would be redundant.

I've tried looking fie a diagram of the '77 R100S, but I haven't been able to find one. It's all for the RS or RT, and the wire colors don't match. When I try looking at the diagrams, I get confused, anxious, and overwhelmed.

Unfortunately, the original owner is no longer with us, and the one who gave me the bike never messed with the wiring.

[20774]

I've tried looking fie a diagram of the '77 R100S, but I haven't been able to find one. It's all for the RS or RT, and the wire colors don't match. When I try looking at the diagrams, I get confused, anxious, and overwhelmed.

Typically, diagrams for the '77 models or in general the /7 models would be applicable to the R100S. Obviously the RT/RS models have fairing mounted gauges, but the rest is pretty standard across that period of bikes.