if you disconnect power to the radio from right behind the radio (just pull harness out) then it must be radio because that's the only thing between power and ground.

if you disconnected isolated radio power upstream somewhere (behind fuse panel or something) and it fixed the problem, then your problem could be anywhere between where you disconnect and ground (at the radio). but that's real hard to imagine because the only place for that current to go would be a direct short from bad wire and would blow the dome fuse.

just pull harness out of radio. bezel is real easy on mine, but it might be possible to give her a reach around to pull the harness out. if you can reach it, and there are 2 harnesses, power is in the bigger harness of the two.

because it's intermittent, i have this creeepy feeling that it's a bum door switch that is intermittent. my first isolated target i think would be to pull the dome bulbs out and put dome fuse back in. i haven't taken a look at the circuit, but i think those go back to the door switches and those are switches that go through a lot of cycles and prob more apt to go bad. but you're whittled pretty far down the road.