Griffy,
I don't think there is any wire harness assembly standards on the public domain. I worked for two automotive wire harness manufacturers for several years. I compiled a good deal of standards for one of them. You'll find that you can sintetize the operation complexity to a set of basic operations: conector assembly, circuit routing, bundle wraping, spot taping, splicing, and continuity testing. Connector assembly has three parameters: sealed vs not sealed (with or without grommet), circuit gage (small gage needs more efford to insert), and number of cavities in the connector (the more cavities, the more it takes the operator to decide where all circuits go to; more than 20 cavities seem to be the treshold). Circuit routing is a function of the length of the circuit. Bundle wraping is a function of whether the wrap is closed or open (candy) and whether the tape is plain or it has a glue backing. Spot tape is unique. Splicing is a function of the joint type: mechanical or welded and the number of circuits. Continuity testing is in function of the number of connections and harness length.
Start with the basic function, then add penalty weights for the complexity. Start by analyzing a small harness; by the third harness, you'll start getting a good idea of what the basic operation time should be and a good feel for the weight compensation for complexity.
Good Luck
