Thanks, jrwb4gbm for the input. All six PLC's are networked to a SmartPanel operator interface ( Power Series 1550 ). The SmartPanel lets the operators enter ram open and ram closed positions for each station using the touch screen. Each PLC is a unique ID, Sta 1 is ID 01, Sta 2 is ID 02, etc. I'm matching ID numbers with the comm software when I try to communicate with a PLC. None of the PLC's respond, either via the network ( 485 link ) or cabled direct to the PLC port. When the netwok cable is unplugged from any of the Station PLC's, the RUN light dies, all led's go off and the PLC is dormant. Power is still applied to the 115vac input but there is no led's lighted, even if I cycle power. If I plug the network cable back into the PLC, the run led comes on and the unit powers up and runs normally. Power is not looped thru the connector, only the two 485 link wires. I have even removed one of the PLC's from the equipment panel and tried to power it up on the bech to see if can get it powered up and communicating... it won't, but when I re-install it and hook the 485 link up, presto up it comes. I'm waaaaaay lost.