It only takes a few minutes to replace. Follow the tube from pitot to gauge and disconnect any cable ties. If it goes thru a cable tray under the gunnel tie one ond of the new tube to the end of the old and pull the new one through. Cut it to length, tie the new tube back up and connect the ends. Be prepared to maybe have to buy a new pitot tube since they often get damaged.
The "wire" you spoke about is probably from something else. Airguide speedometers only have a rubber tube.
I replaced the tube on my 1952 boat a few years ago and she works perfect again.
You can buy the tubing here, but its in a bulk roll. You might try a local marina first. Mine sold it by the foot.
http://www.iboats.com/Teleflex-Pito...55492264--**********.252377015--view_id.40249