Fairly sure. Because it doesn't work with the standard unmolested loom either.

I even put a bulb across the kill switch so I could see if it was getting power, and that lights up.

There is power across all the fuses.

Could it be something in removing the GPS?

Is there an additional ground or +ve 12v that needs to be run somewhere?

it's hard to mess up the kill switch. Black to Black white joined, Red and Red black joined, everything should be powered.