The standard wiring for german fighters separated gun groups and ord to be assigned to 3 buttons. The spitfire pilot in question had his second gun "disabled", I even read pulled out from one source. Which was not standard OP from the factory like Hitech ships his planes to us.
Standard wiring for Luft.
Fw190
A-Knopf - MG & wing root MG151\20
B1-Knopf - Out board MGFF, MG151\20 or MK 108.
B2-Knopf - Drop or launch ord.
Bf109G\K
A-Knopf: 2x MG 131 (fuselage mounted)
B1-Knopf: 1x MG151\20 , 1x MK 108 (engine mounted)
B2-Knopf: drop ordnance
A-Knopf: 2x MG 131 (fuselage mounted) and 1x G151\20 (engine mounted)
B1-Knopf: 2x MG 151 (in wing pods)
B2-Knopf: drop ordnance
A-Knopf: 2x MG 131 (fuselage mounted) and 2x MG 151\20 (in wing pods)
B1-Knopf: 1x MK 108 (engine mounted)
B2-Knopf: drop ordnance