Indeed, actual schematics are needed. Maybe low side switching can be done indeed, actually it doesn't matter that much.
There must be some control hardware that the switch is connected to, and that in turn switches the relays somehow. If I understand OP correctly, the existing controls are to be completely bypassed/removed, and that would mean the switch can be used in isolation.
So now it's time to wait for OP to come back and explain more.