[soundman98]

It really sounds like you 'lost' power on the accessory circuit. There's 2 power wires going to HVAC, and radio. A constant power that supplies enough to have the device do what it needs to, as well as a switched accessory power from the key that's a low power circuit that controls the on/off state.

The next step I would take would be to test for voltage behind the radio to confirm if it's getting the turn-on signal.

In my mitsu eclipse, there was a yellow block with 2 fuses that controlled all the vehicle accessories. During shipping, they yanked the block and it killed all the ancillaries. Many a time I blew that fuse and ended up in the same position you are. But because the fuses were in a different block, they went unchecked a lot of times. The 86 doesn't have that same yellow block setup, but the fundamentals are still there that there's really 2 circuits powering the radio and HVAC.