I had the exact same problem recently, if the little seal on the end of the cable is broken down water can collect in the cable as it dips down before heading up again. Pull off the offending cable, spray some WD40 down there and work it until it's free. Then check that your caliper works, there is like a ratchet system in there so pull on the lever a few times and make sure it stops the wheel. If not then rebuild it with a kit from toyota. Then adjust the handbrake inside the cabin. In my case it was just the cable siezed up.
