try communicating to each board separately, maybe one board is bad dragging down the communication line. on selector board remove cs3b connector. then plug into 25 pin port and see if you can talk to the selector. you won't be able to talk to the door or clc, because with cs3b connector removed, you isolate the board from psc,nsc comm lines to other boards. you can talk to just the selector, if you can talk to selector then thats good, then go to door board, and remove the doc1b connector, try to talk to door board, same idea, you have isolated the psc,nsc comm lines from the other boards, so you won't be able to talk to selector or clc, but you can talk to door board. this will let you know if either of the car top boards are causing a problem. you could also try removing lcc9 connector from clc board, and plug into car top boards to see if you can communicate to them with clc board out of the loop, either way, this will eliminate the boards as a problem. also, is the clc board led on? if not, the power supply may be bad, check for ac ripple on the 5 volt power supply, even though it says 5 vdc with meter, ac millivolt reading should be under 10 millivolts i have seen ac millivot readings of 60 or higher will not allow clc to boot up. good lic