The shredded wires are pretty common. I've actually never had a stick shift 240 that had reliable brake lights, no matter what I did to fix them, until I did something drastic:

I bought a new reverse light switch, crimped female bullet connectors on to two wires, and soldered those on to the switch. The other ends of those wires got spade connectors, and I cut the factory reverse switch wires inside the car, and crimped the other spade connectors on them. I couldn't get the switch, with the wiring, installed in the tranny, ever when I dropped it as low as I could by removing the crossmember. I was using one of those deep O2 sockets with the cutout for the wires, but there just wasn't room to get a ratchet in there. So I dropped the transmission out of the car completely, installed the switch, reinstalled the transmission, and connected up the wires.

Is it a lot of work to do just for reverse lights? Yes. But for the first time ever I have reverse lights that work and don't require a separate some kind of crazy work around.