The wire and spool do not weigh much by themselves. The installation problem is the force carried by the mounting when the wire operates. Attaching it to a thin skin panel would be inadequate, so the spool must connect to solid members within the airframe. This makes the equipment a structural design problem even though the visible device is simple and light.
Notable Point · 2:49:09-2:50:17
Why a torpedo sighting wire needs structural support
A lightweight torpedo sighting wire still needs a strong mounting tied into the aircraft's load-bearing structure.