Typically, the Happ trackball wire harness has two 4-position .156" molex receptacles (although MTA receptacles would work too) - one for each optic board (X and Y) on the trackball. Those two join together to a single a 6-position .093" molex plug (the two +5V and GND wires come to a single pin).
So if you want to make an interface to an Opti-PAC, use this style connector on the trackball, and then make a separate one which has a 6-position .093" molex receptacle, and then have those wires go to the Opti-PAC. That way, to disconnect the whole thing, you just unplug it where the 6-position .093" molex plug and receptacle meet.