To make the fan and current sensor connectors be a true plug in, I needed a form fitting plastic cavity that had the flattened pins in the correct position for plugging in the stock harness.
It must support the connector, align the pins with the harness connector, and will not allow the connector to be plugged in incorrectly.
I made a mold, and after trying epoxy putty, and several other ideas, I found a two part urethane casting plastic, and found that it works great. the cast part is tough and stable. I finish all sides of the cast parts with a belt sander to clean them up.
The first two prototypes look and feel solid.