If it's trying to regulate the voltage using a dump load it has some problems.

 - The dump load is across the source, rather than the battery.  That's OK if it's JUST solar panels.  But it's what's stalling your genny.
 - The blocking diodes between the bridge and the battery are redundant (once the dump load is moved to the battery).  They introduce another diode drop and throw away maybe 5% of your power on a 12V system.

For a quick fix short D7/D14.  (Note that this will cause the "charging" light to falsely indicate charging whenever the battery isn't fully charged.)

Alternatively you could move the hot end of the dump load to the battery - though you'll have extra diode losses things should work OK and your mill should spin up.

The real fix would be:
 - Unhook the hot end of the bridge from D7/D14 and move it to the battery.
 - Ditto the hot end of the dump load.
 - Remove the blocking diode from either your solar panel or your DC generator and use D7/D14 for that function.  Move the controller end of the blocking diode for the other one to the battery.
 - Unhook the hot end of the "charging" light and add small diodes to it from each of the following:  Upstream of the blocking diode for the solar panel, upstream of the blocking diode for the DC genny, and from each of the AC terminals of the AC genny (a redundant small-current version of the top half of the bridge).  Alternatively you could use separate charging LEDs (and current-limiting resistors) for each (though you'll still need diodes from the AC genny - or you could use just one AC line if you don't mind flicker).
Of course that may require surgery on the PC board.