GeeWHIZ, have a look at this article:
http://kc.forticare.com/default.asp?id=376&Lang=1
I am no expert by any means, but I was eventually able to get my FortiGate 60 work correctly in failover mode (actually failover & load sharing mode). I believe the trick you are looking for is that you need to have two static routes defined (one for WAN1, another for WAN2) and two firewall policies (allow everything from internal to WAN1 and everything from internal to WAN2).
My two static routes are defined as:
0.0.0.0/0.0.0.0
10.231.135.73
wan2
10
and
0.0.0.0/0.0.0.0
172.16.2.85
wan1
10
where the IPs are naturally IPs assigned to me by my two internet providers.
It may not be the best setup (as I said, I am no expert), but it does work for me. If you want failover only and no load sharing, then change one of the distances (tens in the example above) to something lower - the route with the lower distance will then be considered the primary one (the other taking over only if the primary one goes down).
Oh... One More Thingâ„¢: to detect if a line is available or not, you have to set up Ping Servers, too. Go to System > Network > Interface and for both WAN1 and WAN2, enter (and enable) a correct Ping Server (use IP addresses of " gateways" your internet providers gave you).
I am using 2.80, so things may be slightly different under 3.00, but three things should still be needed: two static routes, two basic firewall policies, and Ping Server entries.