I bought the cable from Neptune since I could not find one in the store, but what 3dwizard suggests would certainly work.
At the back of the aquacontroller manual is a pin out description for the input connector. Be careful, the Pro has a separate input connector (separate from the serial connector). The aquacontroller II has the input connections combined in the serial connection along with the serial data lines. In this example I am describing the ACIIIPro input connector.
Pin 8 on the input connector is the ground and pins 1 through 4 are the signal lines for switch 1 through 4. So, for example, if you short out pins 8 and 1, then the aquacontroller senses that Switch1 is closed. Same thing for shorting pins 8 and 2 as to Switch2, etc...
So, I just made a little hobby box that the cable connects to with 1/8 inch plugs for each of the four signal lines. Pin 8 runs across all 4 plugs internal to the box. I also included a manual switch for each of the plugs so I could close the connection manually in order to test the switch and to make sure my programming is correct so that the aquacontroller takes the correct action based on the closure of the switch.
Here is a picture of the hobby box with the cable that plugs into the aquacontroller and a home made float switch plugged into switch1 on the hobby box.
Here is a close up of the hobby box:
In my case, I use the float switch to close the connection on Switch1 to make sure the water level in my tank does not get too high due to the LitermeterIII dosing pump. The Litermeter is set to dose just the correct amount of evaporation each day, but sometimes it raises the water in the tank too high if evaporation is less (due to days of higher humidity). The code in the aquacontroller will turn off the litermeter when the float switch rises too high closing switch1. The cod ein the aquacontroller looks like this:
If Switch1 CLOSED Then ALM ON
If Switch1 CLOSED Then DOS OFF
I also turn the Alarm on to let me know something is up.
Hope this helps.
Ken