They're heavily insulated to protect the wire from being flexed too much, and are twisted pair cable to reduce radio interference. I wouldn't try to splice them outside the body.
However, if you pull the carpet up under the driver side of the rear bench seat you should see both cables coming through the floor. If there is enough extra cable there you can extend the regular wire on the other side of the connectors they plug into and then make a new rubber grommet/seal to keep water out of the body, leaving you with more cable outside.