Replacing 30 year old light switch with new light switch assembly need help with the wiring identification (-; thought this would be similar to replacing outlets but all the wires are black so I am at a loss. Thank you. New switch ..basic from Home Depot —one green two brass one black screw
Does not matter what color the wires are. With switches we see far more problems from people applying what they think they know about wire colors and the odd things that are common practice in switch wiring before the requirement to supply neutral to the switch came about. They unscrew everything and then can't make it work because they lost track of what went where.
All black is fine - just be sure to keep track of which black wires go where, and put them the same place on the new switch.
The old switch may not have a grounding (green) screw.
The old switch appears to be a two-terminal switch with one wire on one terminal and two wires on the other terminal. Mark, tape, or just don't disconnect all the wires so you keep track of which two go together.
Connect one wire to the black screw. (or one of the brass screws, but for the sake of a narrative that will work... lets stick with this.)
Connect the two wires to one of the brass screws. Leave the other brass screw empty, since you are replacing a two-terminal switch with a 3-way.
If you need to, connect a short wire to the two black wires that go together using a wirenut or approved splice block and connect that short wire ("pigtail") to one of the brass screws. This is better than using those "push-in" or "backstab" connections that your old switch seems to be wired with.
The green grounding screw should have a green or bare-wire pigtail attached that connects to the bare or green ground wires in the box, assuming you have ground wires (mid 1970's or 80's there should be.) If the box is metal, those should already be connected to the box, as well.