It should work, a few things to check, the modified switch mount might have limited the switch travel, join the two wires on the switch together to see if the pump starts, if it does then the switch needs investigating.
If not, does the courtesy light and horn work, the fuse and holder terminals are a bit notorious for bad connection due to corrosion/tarnishing, may need cleaning, the supply terminal you have used is the permanently live one, not the ignition switched one.
I think it will be one of the above, if not it just leaves the earth, a poor crimped terminal or faulty washer pump
Regards John