Neutral Light

[RickR90s]

Recently completed a new wiring harness install on my '74 R90s. The only new issue is that the neutral light comes on whenever the clutch is pulled in, no matter the gear. This does allow the bike to be started in gear per the intent of the clutch switch, but has two associated problems that didn't exist with the older harness.

1) Neutral light always comes on when changing gears
2) Makes it tougher to select neutral as the light is on with the clutch disengaged


the switch has two wires that I have connected to the Yellow/Brown terminal and the Brown (ground) terminal inside the headlight. My buddy's same '74 R90s has the same two terminals going to the same colored connections in his headlight, but doesn't have the same issue.

My clutch switch has variable resistance (varies between 1.7 ohms and 25 ohms when closed) but I still have the same issue if I run a jumper between the yellow/brown connector and the brown connector (simulating the clutch being disengaged, switch closed).

Any info would be appreciated. I could just leave one wire disconnected (which resolves the neutral light coming on), but the bike obviously won't start in gear. Sort of like to have everything working as designed if possible.

thanks,

RPG

Any help would be appreciated.

[Jean]

On the back-side of your fuse board between the terminals that connect to the wires going to the neutral light AND the clutch switch, there is a diode that should prevent this from happening. The Clutch switch wire should be plugged into ONE side of this terminal location and the Neutral wire plugged onto the other side. From my schematic, the clutch sw. goes onto the same side as the wire from the start sw.
From reading your post, I think you have connected to the wrong terminals. The Brown/yellow wire of the starter switch ought NOT be connected to the neutral sw terminal. The blue/yellow wire from the starter sw. should be connected to the same terminal as the blue/yellow wire from the clutch sw. The wire FROM the neutral light appears to be black/brown and connects to the OTHER side of the terminal set where the blue/yellow wires are connected. The diode is between these terminals. If you connect them opposite, the diode is ineffective and weird things happen. If you connect the start sw. backwards, other weird things happen as you are applying power to places (thru the common terminals of the start sw. circuit) where power should NOT be seen.
DO YOU HAVE A SCHEMATIC? The terminal board usually has a small picture of the diode printed on it, it is position 6 (or 5) counting from the fuse end.
Does the NEW wiring have ALL the same colors as the original? If not, it gets REALLY difficult.
Finally, what happened to the original wiring? It's just possible the diode is failed. they fail either shorted or open. usually open.

[RickR90s]

thanks Clem. I did check the diode and it's forward biased (.7vdc) so I believe the diode is good, but maybe I have the wiring backwards as you suggest.

Original wire harness replaced only as a pre-emptive strike at being stranded one day. It's 40 years old and many parts were brittle with a lot of insulation splitting so I'm glad I did it. I'll check on the wiring when I get home and let you know.

thanks very much,

RPG

[Dave Backmarker]

RPG,
And, if you haven't already, you should ensure the neutral switch is working properly. To do that, disconnect one of the spade connectors from the switch on the bottom of the transmission and shift the bike into neutral. Check continuity with a Volt/Ohm meter and then shift the bike into gear and measure continuity again. If the switch is working properly, neutral will be closed and any gear will show open.

DaveM
1975 R90S, 2000 R1100RT

[RickR90s]

"And, if you haven't already, you should ensure the neutral switch is working properly. To do that, disconnect one of the spade connectors from the switch on the bottom of the transmission and shift the bike into neutral. Check continuity with a Volt/Ohm meter and then shift the bike into gear and measure continuity again. If the switch is working properly, neutral will be closed and any gear will show open".

will do. thanks again.

RPG

[Jean]

By now, RickR90s should have received a simplified schematic I made for him with an explaination of how the wiring can leave the neutral lamp lit when the clutch is actuated. I'm pretty sure that is what has happened.
I STILL do not know how to post a .jpg onto this forum. (Don't bother to explain... Rob tried a year ago...)
I DO believe his neutral switch and clutch switch are working OK tho.

[Deleted User 72]

Jean,

Below the box in which you may type a reply to a post is a bar with "Save draft", Preview", & "Submit" buttons on it. Below that bar is another area with "tabs" on it. Mine shows (2) tabs "Options" & "Upload attachment."

I will leave it to you to figure out which one "Uploads attachments."

[Jean]

OH.
DUH.
I will try it with something...take cover.

[chasbmw]

Did not BMW change the neutral switch and the wiring in and around 1974/5?

[Jean]

Chasbmw: YES. I corresponded with RickR90s off forum and found he had an EARLY 74 bike without the "emergency" stop switch. There was a possibility in the transition time, late 74 early 75, that the wiring was different. Experience also suggests the USA bikes might have been different earlier than the European versions and who knows what. This is ALWAYS an issue when dealing with models that experienced some changes during their model run. I think (not real sure) this may have also been when the neutral switch was changed from NC to NO, but I really thought that was when it was not OUTSIDE the tranny. This one is outside from what I can tell.
I hate it when they do that.