The face of the gear it flat and smooth. You can't even tell its a gear there from the outside. It has a hole in it the gear face that the cable slides into, and the hole is flat, like a flathead screwdriver notch, but its about an inch deep. The ends of the cable are flat, look similar to a flathead screwdriver, and slide into these holes. The nylon covering over the cable has ends on it that are threaded, and they thread onto the body of the gauge and gearbox to secure the cable. The gear spins, the flat end of the cable is secured into the middle of the gear.
The face of the gear that shows through the housing for the cable to slide into is roughly 2" wide.
They DO offer an electrical connector for this gear. It attaches to the gearbox and slides into the face of the gear just like the cable does. You can them in 4, 8, 16 pulse per rotation versions. This would seem like a no-brainer to use, but they're $3500 for the sensor with wiring and digital readout, or roughly the cost of 3 years worth of the cables for the current configuration.
If I could get a motor, sensor, etc that outputs X pulses per rotation, I could make up a bracket and adapter to mount it to the gearbox and attach to the slot in the gear, and save a LOT of money.