Join Date: Apr 2008
Location: Kamloops, BC, Canada
Rep Power: 1
I've used Vaseline as a substitute for dielectric grease in the past with good success. Vaseline is easier to clean than dielectric grease, but it melts at a lower temperature (heat should not be an issue on the back of the speedo). I keep a tube of dielectric grease or Vaseline nearby whenever I do anything on the bike, and I compulsively coat every connector.
Note: Some people say Vaseline when they mean 'Vaseline Intensive Care', which is skin cream. What you want is Vaseline Petroleum Jelly, a translucent greasy substance, not skin cream. Moisturizer is not good for your electrical connections.
Incidentally, 'dielectric' is pretty much a synonym for 'insulating' in this context. 'Dielectric' refers to the behaviour of atoms within an electrical field: a dielectric responds to an electric field by generating a dipole moment (uneven distribution of charged particles), while a conductor allows the electrons to move free of their atoms and conduct electricity. So if you don't have a conductor, you have a dielectric.