I don't know if there are different volume/on-off buttons between the different years and radios, but I recently took one apart to see why the radio won't shut off (like so many 80s/90s era Ford radios with push on/push off).
I grabbed another one from a junk yard radio to possibly fix can't be turned off (which isn't a big deal for me or this car) and also to see if it would help with the inconsistent volume side to side (generally the passenger side lost nearly all volume).
The little pin on the end of the shaft that slides in the white plastic block is broken off, so it can't catch in the off position. Also it looks like the rotary encoder pins are incorrectly touching one of the sets of segments (causing iffy volume on one side for me).
one style of shaft, I have seen 3 or 4, but they all seem to work interchangeably.
video showing that it can't "click" and stay in the off position, except at the very end, and it only takes a little bump and it turns back on:
https://flic.kr/p/pnLHfc
the on/off section of the switch. The little pin at the bottom is broken off the button of the shaft, it should ride in the white block and one press be gated to one side, another press gated to the other. Similar to how the ashtray cover works (which is bigger and easier to see how it works).
it is an "open" when the knob/shaft is extended/in the on position:
and "closed" when the knob/shaft is not extended/in the off position:
pin broken off the left side of the end of the shaft:
rotary encoder segments (hard to get a good picture of, will try again)
the wiper, the top one looks like the fingers are bent and not in the same configuration as the rest:
