Sounds like you have a mechanically held contactor. Voltage applied to 'on' coil pulls contactor in, latch holds contacts "ON". Voltage applied to 'off' coil, or 'unlatch coil. & contacts open.
Are you taking voltage readings with a solenoid type (Wiggy) tester, or a DVM? You may be reading phantom voltages.
Try the CH website tech area for a mechanically held lighting contactor schematic; it has to be close to the old Westy.
