Well, this is a mystery. The way this works is that in a standard system the relays on the NAC card get the + side of the 24 volts from the resettable +24 on the A buss. When the system goes into alarm the control module turns on -24 volts which goes to the NAC module on the C buss. The relays on the NAC card get their -side of the 24 volts from the C buss. That is how the NAC card relays are activated in a standard system. That - side of the 24 volts goes out of the control module through D25. That is why it is cut in a coded system.
I think we have looked at this before but I want to double check. There are two wire jumpers or 0 ohm resistors (depends on the age of the card) on the NAC card that are normally in but are cut for special operations. They go between numbered points 15 to 16 and 29 to 30. Those connect the +24 volts from the A buss to the relay coils.
Verify on your NAC card whether these jumpers are in or cut.
As I recall you said you have a march time card. Plug the march time and signal card in. The LED on the march time should flash for about 1/2 second about every 6 seconds. IF the jumpers are in on the signal card, the relays on the signal card should pulse with the march time card LED. Click click. Putting the system in alarm is not needed, it should just happen.
I found a substitute for the K2 on the motherboard. It is an NTE R14−11D10−24P. These are available from many sources and are around $10. That should get the system to switch to normal power. Right now it is running on the battery charger. I’ll dropbox the datasheet so you can see the picture.