1993 Legacy has intermittent issues with speakers, power mirrors, power outlet, what

Like the title says, my 93 is experiencing some intermittent electrical demons. The car will start and run fine, all the buttons and dash lights up like it’s supposed to. But most of the accessories only function part of the time.

When I got it, all the speakers on the drivers side of the vehicle worked, now it’s only the rear speakers that work and the front passenger speakers only sparks to life every now and again, usually when I’m using my wipers.

The mirrors will occasionally respond to pressing the adjustment buttons, but usually will not work at all. If they do move, it will usually only be in one random direction.

The power outlet/cigarette lighter works randomly as well. It’ll charge my phone pretty consistently, but if I have my phone plugged into AUX in addition to the power, it’ll make a horrible interference sound in the speakers that greets higher pitched as the engine RPM increases. Unplugging the phone from the power cord makes that go away. The power socket will not warm up the cigarette lighter at all.

I’ve checked the wires in my front doors, since that’d explain the mirrors and speakers, but everything looks completely fine. No damaged wires anywhere I look. Fuses seem to be okay. So now what do I check? And does anyone have good writing diagrams for a first gen on this stuff? Thanks

https://www.jdmfsm.info/Auto/Japan/Subaru/Legacy_Outback/1990-1994/

https://www.main.experiencetherave.com/subaru_manual_scans/

I would start from your aftermarket headunit.