Faulty Clutch Switch - completely baffled

[Bluethumb]

The bike is a ‘76 R90S. Recently the clutch switch went out, frayed at the clutch perch, and I replaced it with a new one. The original clutch switch connects inside the headlight bucket with terminals at the connection board. The following year BMW changed the clutch switch to one that plugs into the wiring harness outside of the bucket. Only the later version of the switch is available which comes with a plug. I cut the plug off, added terminals and plugged it into the connection board.

Initially the bike would turn over as it should, bike in neutral, clutch not pulled in, bike would turn over. Now the bike will only turn over with the clutch pulled-in. With the bike in neutral, dash lights including green all lite up, but the bike will only turn over with the clutch pulled in.

I popped the headlight and have checked the connections multiple times including pulling them, making sure they were clean, applying dia electric grease. I pulled the clutch switch from the perch so I could operate the plunger manually. The plunger action is smooth. With the bike in neutral and the ignition on I can push the plunger in and the bike will not turn over. Releasing the plunger, the same as pulling the clutch in, the bike turns over.

The other piece to the puzzle is the neutral switch went out during all this and the neutral light went out. I jumped the brown/black wire to ground and the neutral light comes on. As I understand it this should be the same as the bike being in neutral and when I do, the neutral light comes on and the bike turns over.

I’m baffled why the bike won’t turn over when in neutral and the clutch out. As it always has and should.

[schrader7032]

I've never had to fiddle with the clutch lever switch. From the diagram, it appears to be nothing more than a switch that breaks the ground path to the handlebar starter button...so no start. As for the neutral switch, I can see what you mean that creating an alternate path to ground so that the green light comes on should work fine. Again from my Haynes diagram, the clutch switch seems to connect to the headlight terminal board (#85b) and there's a diode associated with that. This same arrangement seems to be used in the '77 /7 per my diagram. Could there be something wrong with the internal connections and/or that diode?

[Bluethumb]

Kurt,
Thanks for that reply. I’m embarrassed to admit but I’m fairly ignorant about diodes. I know they’re little tubes with a wire going in and a wire going out. ( Electricity and I have never really understood each other.) And I understand they allow current to flow only in one direction. The clutch switch definitely attaches to the connector board inside the bucket. In ‘78 BMW changed the switch to plug into the harness outside of the headlight bucket. The BMW Rider’s manual’s wiring diagram is correct. The Haynes manual confuses the ‘77 with the later wiring diagrams. Took me a little while to figure that one out!

If the diode is bad, would it allow the switch to still function? As I mentioned, I can depress the plunger, bike in neutral, and it will not turn over. Release the plunger, the bike turns over. So to me this indicates the switch is working. But obviously with the bike in neutral and the plunger depressed (clutch handle out) the bike should turn over.

One added piece of info is that the clutch switch operated as it should for the first 6-8 starts. After that I had to resort to pulling the clutch in.

And…where is this mysterious diode?

By the way, I see you’re in S.A. I’m in Fair Oaks. Small world

[schrader7032]

I think between us, we probably still don't have an "electrical" brain! Here is Snowbum's page regarding the starting circuit:

https://bmwmotorcycletech.info/startingprobs.htm

Do a search this page for "diode"...they start near the bottom. In this area he discusses all about the changes to the starter circuit to prevent engaging the starter with the engine running. From what I can tell, if that diode fails, it can create the situation you describe. Maybe your diode is slowly degrading causing the issue. If this is the issue, the diode is located under that circuit board in the headlight! Makes is hard to get to.

Ah, Fair Oaks! You're up there in the mountains where it's cooler!! I'm down in the low lands near UTSA!!