Electrickery !

[Don P.]

1974 BMW R90, 11/73 Build Date, 9/73 Transmission:

I'm interested in how the Neutral Light is illuminated, when the above Motorräd is in neutral, Clutch Hand Lever released, ignition ON ?

Both the Neutral Switches, at the Transmission & Clutch Perch, are Normal Open when in the above situation.

Fused 12V power is supplied to Pin 12 - Neutral Light, in the Instrument Cluster.
A Switched Ground for the Neutral Light, is at Pin 6 - Neutral Light in the Instrument Cluster. I think this is the power source for the bulb.

Simultaneously, Fused 12V power is also supplied to Pin 86 at the Starter Relay.

The Switched Ground from Pin 6, joins with a Switched Ground from the Transmission Neutral Switch.

They connect to Pin LLK Cathode Terminal of the Diode, in the head light nacelle.
The Anode Terminal of the Diode, 85b, splits into two(2)  Switched Leads (power ?)

Following the split, one(1) lead then goes to Pin 50 - Starter Thumb Switch.
Companion lead goes to the Clutch Neutral Switch

The other pin of the Starter Thumb Switch, Pin 85, continues to the Pin 85 of the Starter Relay; combines with the Fused 12V at Pin 86, to activate the Starter Relay and energize the Starter Solenoid. 

It appears to me, that the Diode, Pin 85b & Pin LLK, is Reverse Biased; as compared to Forward Biased... anyone ?

I can't figure out how, with both the Clutch & Transmission Neutral Switches open, the Pin 6 - Switched Ground in the Instrument Cluster, gets grounded; to illuminate the Neutral Light !

I presume that when the Transmission is in gear, the near zero resistance of the Switched Ground to Ground at the Transmission Neutral Switch, is an easier conductive path then, the resistance of the Neutral Light; which is why it is not illuminated.

If this has given anyone a headache, take two(2) ibuprofen with 'One Can' of your favorite beverage and ride away.