If I remember correctly, the pink one goes to a constant 12 volts at the fusebox...like the fuse for the interior light (it's always live). This is so you do not have to reset all the memories or clock on the radio. Basically, it just holds the memory items when the key is off and does not actually power the radio.

The other goes to a swiched item that only gets power when the key is in the ACC or ON position. There is probably a fuse marked for the radio in the existing fusebox that you can use for that one.

Screw on the back of the radio could be a ground, or a mounting point for a bracket to hold up the back of the radio, or an antenna trim screw. I think the trim screw only works for AM though. Antenna trim screws are pretty small.

Hope it helps
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'60 544, '68 220S, '70 145S, '72 144E, '86 745T