This is a BIG truck, on the ones I have seen, they have a few "hidden" in line fuses also, wrapped up in the wire harness.
BUT,,, A correct model and serial number will be necessary to get a better guess where to look.
Jerry, when you say you "had a broken joystick controller", can you describe a bit further how (in what manner) it was broken? Did the lever fall off, or was it in the 'controller' itself? was it not lifting or not tilting? is this truck equipped with an empty container handler? does this unit have error codes where the hour meter display is?

Are you sure of the model- the XL series I'm familiar with don't have seat sensors nor computers.