On page 4, there is an "IDE Power" connector. It looks a lot like a 4 pin CPU fan connector, but it (obviously) provides different voltages that are appropriate for 3.5" IDE drives (5V ...

Each of these trailer 4-pin connectors comes with unique wiring diagrams. It can be a real pain to have failing wiring in your trailer. This can lead to dysfunctional brake lights, turn signals ...

Often refers to the 4-pin connectors used to attach DC power to the drives inside a PC cabinet. Molex is a large manufacturer of electronics plugs and sockets that dates back to the 1940s.