Another issue somewhat common, this aint what your dealing with on this issue but could help someone else someday, if the toggle switch in the COP goes bad, you loose 24v on p24c. If you loose p24c, it looks like everything else is powered and on but you will not have comms on your laptop. You MUST have 24v between pins 1 and 3 on the connector on the elevator for communications to work. Even if the comms voltage is on 5,7,9,11for nsc and psc, gotta have 24v on 1 and 3. The toggle switches suck. They have 3 poles in them and will have only 1 pole (usually p24c) go bad but the other 2 work.
When working you should have approximately .7v between pins 5-7 and 9-11. It's a type of 485 which works off a voltage differential similar to how can operates. .7 at idle is what I've read with my meter on working cars as a very quick check to see if the comms have an issue or not. Pin 1 is 24v, pin 3 is ground.
