I've helped debug several Fleetwood/BIRD system failures and all of them have had one of the following causes:
1. The isolator relay has failed. Simple to check: (1) Plug into shore power, (2) Give the BIRD a couple of minutes to engage the isolator relay, (3) Verify nominal +12 at the isolator relay coil, (4) Measure the voltage drop across the isolator relay contacts, which shouldn't be more than a tenth or two.
2. The fuse between the chassis battery and isolator relay has blown. One way it blows is when one of the two batteries is seriously run down and the other is charged. When a charging source is applied to the already charged battery, the BIRD engages the isolator relay, a few hundred amps flow from the charged battery to the dead battery, and "pop" goes the fuse.
Anything is possible of course, but I've not seen any failures of the BIRD module itself. Where Fleetwood hid the fuse I'm referring to, or if it even exists in the OP's rig, I wouldn't know.
