A fuel injector system comprising a universal fuel injector assembly having a universal electrical receptacle, and a family of specific adaptors for connecting the universal fuel injector assembly to a corresponding family of specific engine harnesses and/or design layouts. The universal fuel injector assembly has an injector tip and fuel rail tip compatible with the engine and fuel rail sockets of a plurality of engines. Each adaptor comprises a fuel-injector plug at a first end for mating with the electrical socket and a harness-specific plug or socket at a second end for mating with a specific harness socket or plug.