It's not a new home for my non-existent bike, but.....

[cd34]

Having done more than enough wiring to last a lifetime, run new cable to those two. Rather than try to troubleshoot, you'll save time just putting a new one in. If you just tossed the wires into the attic, you could use the existing wires as a pullwire.

Then call your exterminator to get rid of the critters, or your contractor to find out who put a nail through the wire.