Steve,
I don't think that you have correctly traced the circuit. If you connect the pressure switches to the overload relay contact, they would have no function. You have just connected a number of switches together without a load or source. Also the OL contacts only open when the motor has been overloaded not when the motor starts and stops. Are you sure these switches are not connected between the power source and the hot side of the coil(term 3)? On most starters you can add at least 4 auxiliary contacts in addition to the motor power contact and the NO seal in contact (terms 2 and 3).
Don
