Help with electric wheelchair motor-controller?

I recently bought an old Invacare wheelchair to use the motors and controller to integrate with a computer. However, the "MKIV INT" (i'm assuming that's the manufacturer) motor-controller is an all-in-one with the joystick in it. I removed the joystick, hoping I could connect to a DAC and my computer via parallel port, but the joystick has a small circuit inside of it. I'm assuming the circuit gets 5V from the controller and sends pulses of the analog joystick position. I was thinking about de-soldering the 4 wires from the joystick (2 wires for x-position and 2-wires for y-position) and first try to replace the joystick with an old PC-joystick--just to see if the controller detects different resistances of a different joystick, etc...

Hi. Not sure when you posted this question, but see this thread:

As for the joystick you have, I believe it is an Innvacare joystick. they still have a lot of documentation on their site.