One half-connector terminates leads in the ballast, carrying electricity to and from the ballast coils. Another half-connector terminates leads outside the ballast, connected e. g. to carry power to lamp sockets. A hook extended from a first of the half-connectors engages a catch formed in a second. A retaining surface, preferably associated with the second half-connector, keeps the hook engaged with the catch. Preferably the space between the retaining surface and the catch is smaller than the unstressed dimension of the hook barb--but during the act of engagement the barb deforms to pass between the catch and surface; then the barb springs back into shape and is held behind the catch. In this process also preferably the retaining surface cooperates with the first half-connector to support the shaft or beam of the hook at both ends--as in a classical double-ended beam spring structure, contrasted with a cantilevered spring in a conventional hook and catch. A ramp guides the hook between the catch and surface even if the hook has been warped before assembly, at least in commonly occurring modes of warping.