Hi Virtual Wrench,
Thanks for the diagram, but we ain't out of the woods yet.
I took out the switch and tested it with tester made from an 1156 turn signal lamp. In the LOCK and OFF positions, no juice goes from the yellow circuit 37 [BATT pins] to any of the pins. Check.
In the ACC position, I get juice to both Bk-Lg circuit 297 [A1 pins], no juice to any other pins. I think that is good.
In the RUN position, I get juice to both 297[A1]; R-LG circuit 16 [pin 11] (which is identified on your diagram as feeding the alt. indicator light); and both GY-Y Circuit 687 [pins A2].
In the START position, I get juice to BR-P circuit 262 [pin 12] (which is also identified on your diagram as feeding the alt. indicator light); and to R-LB circuit 32 [pin ST], which goes to starter
In no position of the starter switch do I get any current to pin P1, circuit 977, which feeds a wire that is labeled P-W in my Chilton manual but looks mover like brown and white to me. This seems sorta suspicious. In the manual I can trace 977 to a cryptic little figure that is not labeled, but it has a zigzag symbol in it like the one in your diagram's alternator warning indicator figure. Could this be the wire feeding the indicator? The other wire going to this figure is circuit 640, elsewhere labeled as "warning lps feed."
Also in no position do I get any current to BK-LB circuit 41 [pin P2}. And I don't know where this circuit goes.
After testing the switch, I moved to the ignition switch wiring harness connector. I re-hooked up the battery cables, then jumpered from a hot BATT pin to R-LG circuit 16 [pin 11]. The alternator light comes on but NO current to regulator I terminal.
I removed that and jumped from BATT to BR-P circuit 262 [pin 12]. Same result: alt dash light on, NO current to I terminal.
I thought, maybe circuit 977 is relevant. So I jumped from BATT to pin P1, circuit 977, Nothing. No idiot light, no current to terminal I.
I then jumped BATT to both circuit 16 and 977. Yes idiot light, no current at terminal I.
Back before I took the switch off, I hooked my test lamp between the battery + terminal & the regulator harness I connector. With key off, the test lamp glowed and the dash alt indicator was on. With key on, the test light glowed much more dimly, and the dash light was off. This would seem to indicate the wire between the I terminal and the dash light is OK.
But, the jumper test at the switch harness connector would seem to show that the wire between the switch and the dash light is also OK.
So, I am now thoroughly mystified. Why the hell is there no current getting to the I terminal??? Any ideas on how to proceed from here?
Sorry this is such a can of worms. It is getting just a wee bit frustrating.