Maik is right, no need to give up so soon (thanks!).
Even if the running FGT' s interface IP address is not in the default subnet of the second FGT, you can make it work by the help of ' poor man' s routing' : define an IP pool on the interface connected to the second FGT and source-NAT the traffic.
Example:
the active FGT has 10.11.12.12 on ' internal'
the second FGT has 192.168.0.99 on ' internal'
Both ' internal' interfaces are connected via a switch.
On the active FGT:
Create an IP pool with one address: 192.168.0.88
Create a policy ' internal' ->' internal' , source: ANY, dest: IP_pool
Now, traffic from the active FGT' s ' internal' interface will seemingly come from the same subnet that the second FGT uses. Thus, the second FGT will not have to use a route back. You should be able to connect to the second FGT via
https://192.168.0.99 or via ssh (the default admin methods).
good luck!
Ede Kernel panic: Aiee, killing interrupt handler!