With that wire disconnected at the alt. I see 12 volts with the key in position II - you say that should be at ground and then go to 12v once car is started?
• I'm still not clear where you "see 12V". If at the disconnected wire, that's good. If at the (empty) D+ terminal, not good — it's supposed to be at ground for the warning lights, before starting.

Hmm, I have to back to basics because I thought the circuit went from battery + to ignition switch to warning lights to small terminal on alt.
• Right, and then thru alternator (Vreg, brushes, exitation winding in the rotor, then to ground) to allow exciter current from lights to do it's thing when the alternator gets turning.
When the voltage comes up, D+ rises to the same as B+. That puts 12V on the "alt side" of the bulbs, so with 12V on both sides (the orignal switched 12V is still on the "switch side") there can be no current flow, so the bulbs go out.

Again, what year is your car?

And where in Bentley are you finding your warning light (single bulb) circuit. The other 3 are connected in parallel with the Batt light thru individual diodes. Wiring Diagrams in section 390 show this.
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Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.