Since you are having multiple problems at once, I would start looking at grounding for the systems being affected. If you can get a print of your wiring system from Mitchell's or the like -- I have purchased manuals from the dealer before and they are expensive, but the cost is offset by not paying someone else to fix it -- see what these systems share in common.
I had almost exactly the same problem with a Nissan Z car, and it was driving me crazy. I spent hours tracing it down with a Mitchell's diagram. Nissan likes to tie their grounds together with copper crimp rings. They will join several small ground wires, like 12 or 14 AWG to one larger wire, like an 8 AWG and take that 8 AWG back to the main ground bus instead of running a bunch of smaller wires in a harness. I finally found my problem in that they had done this within a harness, but had not crimped the copper ring around the wires they were trying to join. It held for several years and then finally started losing contact. I had to untape the harness to find this, but did most of my research on the problem by analyzing the wiring schematic, looking for that "common element" instead of haphazardly tracing out wiring, hand over hand.
You also need to check the problem while it is under load. In my case, if I turned off all the items that were being affected, there was enough conductance through the connection that I was reading 12 volts on the circuit, but when I loaded it down, the resistance of the bad connection came into play and the voltage dropped off.
The main thing is, it will be difficult to shoot the problem without a schematic, but once you do get one and if you find a common ground for all these things it could become obvious. Of course, it could all be in some failing control module in common, too.
Just a thought...
Good Luck!! Even though I work as an electrical testing engineer, I hate electrical problems, especially intermittent ones!
eti engineer