Hello All and thanks for your replies, I really appreciate it.
Here's the latest, and no, it's not solved yet, but I haven't been online checking your suggestions for 2 days. Oh, and there really isn't a way to "go back" with the original head unit without a *lot* of work -- the original harness was cut off because we didn't think we had an adapter for it. Reconnecting the harness wires would be really difficult, if not impossible now. :(
I contacted my original dealer for some ideas on the fusebox and he said the label is bad, but is supposed to be correct. I don't get it...it's "identical" to the other label. He suggested I go to a nearer dealer and see if they'll let me make copies of some key pages from their trouble shooting and general manuals. I tracked down seven pages with circuit diagrams involving both the instrumentation lighting and the audio system. I'm pretty grateful they took the time to help me out...
So, armed with the diagrams I tried connecting the wires, and discovered no difference at all. I have one titled "Lights Brightness Control" (sorry, no page number visible). It shows the dimmer knob on it's own circuit to the multiplex control unit (Driver's). Then another circuit coming thru from the combo light switch joining up with a separate multiplexor circuit (RED / black) to both the guage lights (4 bulbs) and a list of other lights (including the audio unit, clock, gear position, cruise main switch, hazard switch light, and heater control panel light.
On a more detailed diagram, it looks like there are 6 bulbs in the cluster that are in series, but connected in parallel to a stabalizing circuit, gear position indicator and lcd back light. I didn't think I'd need more details on the multiplexor but what I do have shows a dedicated circuit to the dimmer and power going to the heater control panel, I think from there to the rest of the lights in parallel with the instrument cluster grouped and finally back to the multiplexor. (criminey, a picture really is worth a thousand words cuz I'm sure doing a poor job of this). The guage assembly lights part of the diagram are enclosed together as well with a single power line coming in. However, since the clock and hazard switch lights are in parallel with this, and also are not on when I expect them to be, perhaps the problem is more up-stream?
I checked the fuses figuring I might have blown one by now, but nope. I even picked up a tester and checked every one of them to be sure they really were ok still.
Now that I have removed those fuses from this, perhaps something's up with the "stabilizing power circuit" in-line somewhere. Is it possible that the lighting elements are tied together when the parking / head lights are on in a way that would cause a single bulb to deaden the circuit? The gear indicator, odometer, clock and green ventilation indicators are lit up. When I put on the headlights, they all go out except the ventilation indicators (AC on/off, vent position) which dim signficantly, but are somewhat illuminated (even with the radio powered off to be sure it wasn't providing some kind of backlight).
I'm at the point now where I want to check the guage lights, but discovered that removing the cluster is difficult given that the steering column cover keeps me from completely removing the trim around the cluster.
Oh, and thanks for the owner's manual tip -- I found better diagrams than I thought I had a few pages after where the index pointed me -- serves me right for not leafing thru the thing page by page.
It also sounds to me like I should disconnect the two wires now that it hasn't made a difference to avoid causing a short-circuit once the problem is really resolved. And I'm starting to think that the multiplexor is fine, otherwise I don't think most of the components would light correctly. I'm way outside of my bailiwick though...
As usual, any and all suggestions are welcome.
rjs