There is no ground for the smoke unit wiring, so where does that wire go? It's likely not used with the PS/3 upgrade.
Note that for PS/2 or PS/3 electronics, there are NO chassis ground connections except for the input track power on the 7-pin connector on the PS/2 or PS3/2 board. You have to make sure no other connections get grounded, that will be very bad for the electronics.