I've got two old RFU adapters that are compatible with N64/Gamecube
consoles... Both work, but one was missing the pin that actually
connects into the back of the television's analog input jack. The
other had a damaged head and I could not plug it into the analog input
jack either.

On one, I sheared off the rubber and smaller copper wires, exposing
the main copper wire beneath. I'm a complete novice with this kind of
thing, but after no luck attempting to plug the copper wire directly
into the analog input jack, I assume the smaller copper wires are
actually needed.

At this point, both have the heads removed from the cable.

Any suggestions on this?