A waterproof splice for use in connecting two multiconductor electric cables having jackets of different insulation material and a method of making the splice are disclosed. The splice consists of a mechanical electrical connection between the conductors, a mechanical bond formed on the insulation of one of the conductors and a sheath of insulation material molded over the splice and adjacent cables. The sheath bonds with the jacket of one cable and the mechanical bond formed on the insulation of the other cable. The mechanical bond is a seal ring of elastomeric material that is compressed between glands to move the seal ring into sealing engagement with the conductor. The disclosed splice is both strong and waterproof in spite of the poor bonding characteristics between the two different insulation materials on the two conductors. The splice is appropriate for cables having surface, subsurface and underwater applications and is specifically designed for use in conducting seismic surveying operations.