I've just received my Happ trackball, and I'm wondering if anybody can help me with this problem. The plug on the trackball (a re purposed and refurbished Golden Tee ball) is different from what my IPAC2 is expecting.

Groovy Game Gear has the
Trackball Cable for Opti-Wiz™ "No-Solder" cable that replaces the Molex harness you are holding in the pic and connects the two green optical boards (P/N A052-1010-00) to the Dupont pins on your
I-PAC 2 I-PAC Ultimate I/O encoder.
What are the pinouts of the Optic Sensor pcb A052-1010-00 and A052-1011-00 used on the trackball or trackwheel or 360 steering wheel ?
These alll use the same Item # A052-1011-00 Optic Sensor Board. The connections are as follows.
Pin 1 - Output A
Pin 2 - +5V
Pin 3 - GND
Pin 4 - Output B

The image above shows the newer red optical boards (P/N A052-1011-00) and an Opti-Wiz, but the trackball cable will work the same way for your encoder -- just lift the tiny lever and pull the female ground pin out of the 5v/ground Dupont housing since 5v and ground aren't on adjacent pins.
Trackball pins are top center, just left of the LED power jack.
5v to 5v.
Gnd to G.
X-axis data lines to X1 (purple) and X2 (blue) -- if the axis moves backward, swap the data lines
Y-axis data lines to Y1 (yellow) and Y2 (green) -- if the axis moves backward, swap the data lines

Scott