I had the same problem last year but this year everything is working fine.I bought some connector cleaner at radio shack and put some in the connector.I plug and unplug the connector 9 to 10 times and now everything seems to be working fine.
But when the problem comes back, I would spend a couple of more dollars more and get the Star Gazer Upgrade . It is a Perfect Pass upgrade that uses GPS instead of water and the wheel paddle to indicate the speed of your boat. No more problem with speed sensor under the boat.
Apparently it is a simple job that takes 5 minutes max, unplug the old Perfect Pass module and replug the new module with the GPS Antenna. It runs for about $480.
Here is the link...Hope this helps
http://www.perfectpass.com/pp_star_gazer.html#upgrade