On my 1957 Chevrolet Nomad we don't seem to have enough of the plastic plug sticking out of the rubber firewall harness gromet going toward the engine to plug in the engine bay side of the wiring harness together . Do not want to trim the rubber gromet , to try and make it thinner . There dose not seem to be any plastic lock clip in the plug ends to lock the two together . What keeps them locked together ? Any help appreciated .