2002 Buick Century 3.1 Cranks.. and starts momentarily. BCM code question.

Here's what I have for today..
Bottom line no power to IP panel A3&4 ( or 5&6) 
And H works in Start but no voltage at Run. 

Still have the  P1626 in the PCM and B1477 in the BCM..

 
If you are back probing this yellow wire directly at the ignition switch connector and only have power while cranking but not in the Run position, then there is a problem with the ignition switch.

I'm starting to feel like Ivan @PHAD.. 
Just to make a record of this step and planned next step.

I ordered what I thought was a switch but was actually the harness so after replacing the 8745 harness still nothing at IP panel A3 on the yellow wire.
Do I look at the key cylinder as suspect next?
I'm going to try a wire signal tracer next though up in the dash seems crowded and obstructed.. I guess I can check how many connectors are in the path..
On the other side of the firewall...
The only voltage on the ICM harness connectors is the UH box fuse25 elec IGN power supply.  fwiw.

New switch was installed and no difference. Still have 0.0v at Run and 12v at Start.
I have a new key lock cylinder in hand as well but my scan tool is reading all the Key associated pids from Security and Class 2 from the OG key just fine.
It shows the key in Run when it is.. which is part of this question I have.. is the key lock cylinder acting as an actual switch (electrically speaking completing a circuit) ? If the modules are communicating with it with no complaints what's interrupting it in Run position?
the Switch (part 8945 under the column) is comprised of a sealed switch box , wire harness and connector and has continuity underload of a 3A test light to the IP panel A3 fuse terminal so it will hold the voltage when there.
Any suggestions?
Anyone?

The lock cylinder does not carry any current. It is essentialy a finger pushing a button, your finger doesn't carry any current when you push the window switch to make the window go down, if that makes sense.
You could turn the switch in the box with a screwdriver and should still have voltage on the yellow wire in start or run.
Are you back probing at the connector on the yellow wire with the switch plugged in, or are you still measuring at the fuse panel?

We just acquired a 2002 Buick Century with a 3.1L engine for resale at my shop. I am willing to perform some comparative tests on this vehicle possibly this weekend when the shop is closed if it will help you out.

Thanks for that assurance I couldn't see how it would carry current but with a new actual switch (8745) installed and no joy the key lock was the last thing to eliminate at that end.

As to probing, I was back probing the connector and the back of the IP panel since I have it out to better investigate.
I appreciate the offer for donner car testing.
I'm more than happy to run tests but feel like I have run out of ideas or more apt like a dog chasing it's tail.. oof oof

All of the testing I have recommended was to be done at the ignition switch connector, back probing with the connector plugged in. I really cant make that any more clear.
You're not proving anything we don't all ready know by continuing to test at the fuse panel.
You know there's no power at that fuse, that's why you need to move further up the circuit and check the source.

Back pinned the new switch and same results on the yellow wire.
0.0v @ Run
12v @ Start

 
It defies logic that both switches would fail in the exact same manner, but like I mentioned before, we have to trust that you are performing the tests correctly.
According to the diagram I have attached earlier, the yellow wire labeled D1 on ignition switch connector c201 should be hot in run or start.
Assuming the diagram I have attached is correct, which I believe it to be, and assuming source voltage from the fuse is good (which it must be to have power in Start) with the ignition switch in Start (being engine cranking) or with the ignition switch in Run (being the position the switch defaults to after releasing the key from Start) there should be power on the yellow wire labeled D1 while back probing the ignition switch side (not the body side of the harness so as to rule out a terminal issue in the connector) of connector c201. It is a straightforward switch circuit, the only fault can only be the switch itself. There are no more trouble shooting steps for no power on D1 in Run and Start.

Sigh..second attempt to sign on and reply here.

Thanks for the reply and that's what I thought as well, I'm at amateur diy electrical diagnostics level here and trying to follow the training and methods I've been studying here and elsewhere.. lots of lectures and case studies on YT.. but this is my lab time project it would appear.

While waiting for the next switch to arrive in a day or two, as a tes.. what if with the og switch installed, I jumped a fused 12v to that IP panel terminal then check the codes again to see if it was causing the BCM B1477 low voltage on circuit issue?
Would that in a sense show that the codes are secondary to the apparently faulty switch?

 

 
So maybe we're not exactly on the same page, I have the Buick in the shop right now for front end work and decided to poke some fuses.
If this is the fuse you are saying has no power in run, then that appears to benormal. The car is running right now.

That is the fuse. I guess I can check the BCM for it's power at B9 .. as that's where the codes are seemingly being generated.
I'm also replacing the Cam sensor this afternoon after checking it yesterday and finding hen scratch for a signal.
If that doesn't help I guess a new BCM is really what is needed. Unless someone has another idea.
Thanks for checking on the circuits!

Instead of the BCM I started back with testing the cam and crank sensors and found the cam sensor was bad and replaced it and continued to check the timing of the ignition starting sequence as described in the service data. I had disconnected the bat neg cable to install the switch at least twice, leaving overnight once.
That may have effected the ECU\BCM but at any rate it it fired up and runs.
Still has the RAP relay code though.. so that mystery remains unsolved.