A system for making up wiring harnesses includes a base harness having a set of flexible multi-conductor cables and a set of supplementary wiring harnesses adapted to connect in a particular location of said base harness. The connection area does not have a multi-conductor replaceable connector to the base harness, so that the cost of unused connectors is not incurred. Each supplementary wiring harness connects to a reserved location. The reserved locations may be shared between mutually exclusive options.