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Hello all! I have a 1994 R100R Mystic. Something strange happened the last time I rode it. It started with the Gen lamp coming on when bike was shifted into neutral. Then all of the instrument lights stopped working. The fuse was blown. Does this sound like it could be the neutral switch? It has been leaking trans oil out of the switch. Any advise would be greatly appreciated.

It won't be the neutral switch... the worst case scenarios for a failed neutral switch is that either (a) the neutral lamp won't light at all or (b) that it will be on all of the time.

It sounds very much to me as though there is a short circuit between the wire from the neutral switch to a 12 volt circuit (post fuse). Unfortunately, the wiring diagram in Haynes is singularly badly drawn and unhelpful but, in my opinion, the most likely place for the two sides of the circuit to come into undesirable contact is in or around the instrument panel.

A good testing technique for a blown fuse caused by a suspected short is to temporarily wire a 12 volt bulb (not an LED) in place of the fuse. You can then switch the various circuits on and off to see which one makes the temporary lamp glow brightly. In this case, I would expect the lamp to light when the neutral switch is closed.

Oh, just one thought... check the neutral bulb. It's unusual but possible for the bulb to fail short circuit. if it does, it will cause exactly the symptoms you describe.

Hope that gives you some ideas...

Rob

I would think that if it were a short, it would be after the neutral switch since engaging neutral causes the GEN light to go on. If you takes the wires off the switch, one will have power when the ignition is on. The second goes to the light and provides power for the starter. If you leave the powered one on the switch but remove the other, check to see if the GEN light still comes on in neutral with the engine running. If not, you’ve narrowed down your search to the disconnected wire and where it goes.

UPDATE: I went out to my garage and looked at a Clymer manual I had that covered the bike. Unfortunately, for the R100R and R100GS, it shows only a single wire going to the neutral switch. That wire goes to the starter relay, similar to the older bikes. The bikes does have 2 wires going to the switch. I looked at my R100R Mystic. The wire comes out from under the trans on the left side and follows the frame up toward the battery box. In that area, there is a connection. Two wires. Brown/Black and Brown/Green. When I disconnected the wires, the neutral light went out (as expected). What was unexpected was that both wires on the chassis side (not the switch side) had power, using a test light grounded to the motor. I assumed one wire (the brown/green) would have been powered while all the wiring diagrams I've looked at shows the brown/black wire going to the starter relay. I didn't expect to be getting power from there, especially with the clutch engaged. Not sure on the R100R, but the older /7 have a diode behind the fuse block in the headlight which prevents power from the clutch switch from powering the neutral light. Bottom line, I haven't given you much.

Seth wrote: ↑Fri Mar 20, 2020 6:18 pm
UPDATE: I went out to my garage and looked at a Clymer manual I had that covered the bike. Unfortunately, for the R100R and R100GS, it shows only a single wire going to the neutral switch. That wire goes to the starter relay, similar to the older bikes. The bikes does have 2 wires going to the switch. I looked at my R100R Mystic. The wire comes out from under the trans on the left side and follows the frame up toward the battery box. In that area, there is a connection. Two wires. Brown/Black and Brown/Green. When I disconnected the wires, the neutral light went out (as expected). What was unexpected was that both wires on the chassis side (not the switch side) had power, using a test light grounded to the motor. I assumed one wire (the brown/green) would have been powered while all the wiring diagrams I've looked at shows the brown/black wire going to the starter relay. I didn't expect to be getting power from there, especially with the clutch engaged. Not sure on the R100R, but the older /7 have a diode behind the fuse block in the headlight which prevents power from the clutch switch from powering the neutral light. Bottom line, I haven't given you much.

Assuming this part of the wiring to be the same as the other airhead neutral switch wiring setups, there are two wires to the switch. These go into a sub-loom which, as you say, runs alongside the rear frame tube to a two pin connector... however...the two wires in this connector are not the same two that come out from the neutral switch (or rather one isn't).

The wire from the oil pressure switch also goes into the same sub-loom.

The brown/green wire is the oil pressure switch lead, the brown/black wire is the neutral switch lead. The second wire from the neutral switch exits the sub-loom in the vicinity of the left front footrest and connects via a ring connector to the lower left gearbox bolt. This wire is a permanent ground. With the two pin connector disconnected, both the brown/green wire and the brown/black wire will show battery voltage via their respective bulbs.

As I said above, the Haynes diagram is badly drawn... the Clymer version is even worse... but from what I can see, the seperate diode used on earlier models is within the starter relay on the R/Mystic and later monoshock models.

Rob

So I've looked again at my Mystic and the wiring diagram.
Rob is correct, as expected. By the battery box is the connectors of 2 wires, as I mentioned before. They are the "grounds" to the oil pressure and neutral lights. The wires travel down the frame into a slightly larger bundle. As they travel forward toward the front of the transmission, a brown wire (unwrapped) comes out of the bundle and grounds to a transmission mount bolt. Then the bundle splits into 2 smaller tubes. One contains the single wire to the oil pressure (brown with a green stripe). Makes sense since brown is ground, these are the ground side of the indicator lights. The other tube contains 2 wires, the brown with black stripe and an all brown. My assumption is the brown wire from the neutral switch, travels up the bundle and makes a u-turn to come back out to the transmission mount bolt.

Therefore, a bad transmission switch cannot be the problem, since it indirectly (through the brown wire) grounds the brown/black wire. If the switch internally grounded, the light would just be on all the time. The oil pressure switch has 1 wire and the switch grounds itself to the engine case. Why didn't they do something similar with the neutral switch, eliminating 1 wire?

The Mystic, unlike a lot of other bikes, has a plate which holds the instruments and is mounted to the upper triple clamp and holds all the lights. Behind the plate, all the lights' wires are exposed. Look at the fiche (62_0257 - DASHBOARD SUPPORT) part #12. No housing. I didn't look at this again, but I think these wires are wrapped in cloth tape. Power comes from the fuse to the panel to power 3 of the lights, including the oil pressure and neutral. There is a wrapped pair of wires that come up to the neutral light: one from the fuse and the other goes to the starter relay, which then goes to the switch. If in that wrapping, the wires short to each other, it would cause the problem you're encountering. In the past, one of my lights did fail. I thought it was the bulb, but it was a broken wire in those exposed wrapped wires. I would remove the panel, unwrap the wire pair for the neutral light and look for a short between the 2 wires. Any grounding of the "ground wire" from the bulb to the switch would just light the bulb all the time. The only thing that could cause the fuse to blow when the bike is shifted into neutral is a short between these 2 wires to the bulb. I didn't look where the plug side of part number 12 (WIRING CONTROL) plugs in, but it could be on the bike side of that plug.

Seth wrote: ↑Sat Mar 21, 2020 10:01 pm
Why didn't they do something similar with the neutral switch, eliminating 1 wire?

My guess is that BMW couldn't source a switch that grounds to it's body for that function... most of the switches and electrical components used by BMW on the bikes are stock components. It is probably cheaper and easier to use a stock switch than to commision a bespoke component...

Rob

Thanks Guys!! I really appreciate the inputs. I replaced the neutral switch. That needed to be done anyway. That was a pain in the ass for sure! The rear engine mount is a very tight fit. The switch was leaking badly. There was a broken fuse also. The original fine wire fuses are fragile. I replaced all of the fuses. All appears well except for the recurring problem with the left signal cancelling at idle. She is back up and running well though. I don"t know if there is a schematic for the Mystic, but it is a bit different than the R100R. Thanks again to all!!

I don't think that the Mystic's wiring differs from that of the R100R. I had an R100R years ago and I customised it with the instrument panel from a Mystic. The two gauges, the ignition switch and all the lights plugged right into it. Different panel, same contents. Nothing else electrical on the bike should be different.

Yes, I was curious about the statement that the wiring was different.
Went to the fische and other than the instrument wiring, both the R100R Roadster and Mystic were the same.
I know the two bikes have different rear subframes, both mufflers, battery covers, handlebars and seats, including the Roadster grab bar and rear handle (not included with the Mystic). And obviously the instruments. I believe some of the Roadsters only had a single front disk brake.

Seth wrote: ↑Sat Mar 28, 2020 10:05 pmI believe some of the Roadsters only had a single front disk brake.

Very few had the single rotor, and only some very early ones from what I've gathered.