The controller PCBs are part of the FBH. From what I understand, the D1 & D2 were fitted with a CAN bus Themo Top C/Z, remotely started by 12v+ to pin 1, or 12v- to pin 3 using any 12v relay RX/TX module, depending on the PCB.
The D3 & D4 were fitted with a WBUS Thermo Top V that requires a...