@dan2see I forgot to add:
I can shoot the gun, in fact I just shot down an F4 Phantom.
When I click the MASS button, both busbar indicators turn black.
But the rotary Weapons Selection knob does not turn. I tried keyboard commands to select RP/PB but nothing happens.
Is there another button or condition that I haven't done?
Just to add that I had a response in the x-plane.org forum from one of the Thranda team, who made a suggestion. It seems the throttle gate logic is causing me a problem, maybe I can reduce the idle in the acf file.