GGC,
If your system is like mine, any relay can be plugged into any port on the main card. As an example, this means that relay that is in the Aux 1 position could be connected to the Aux 6 port on the main board.. If you have not already done so, then I suggest that you follow the coil wire on each relay and make sure it is plugged into the right location.
The relays in my system are controlled by 25 VDC from an IC chip.. These chips can go bad, but generally don't all go bad at once, so it might be possible to find a working relay and rewire that relay to be the blower relay.
Thanks,
Jim R.