Crikey,
Looks like a birds nest.

Sorry.
Looks like you really need to tidy that up for find your way around a bit easier.
Do you have a multimeter?
If you do, I would test each wire from the microswitch to the IPAC to make sure there is a circuit.
You could get really picky and while you have one end on the microswitch, test the other end on every socket on the IPAC to see if you have your wires crossed, LOL. Won't take that long.
Also make sure you have the wire on the correct microswitch tab, easy enough to do. I have done it loads of times.
I still wouldn't worry about the dedicated shift key.
Using the IPACs inbuilt 'shift' function is by holding the P1 button etc is good enough IMO.
Then again, its your machine.
Good luck, things like this can be frustrating but take your time and you will find the problem.