VPX & Int/Ext Alternator Control on My 914

According to the diagram, the EXTeranl ALTernator is Always connected to VPX(+).
The INTernal ALTernator is also optionally connected to VPX(+) through a relay.
Under normal operation, BOTH ALTs will be in the Connected state.

The secret is in the Lower Right corner of the diagram.
In a 914 there is NO mechanical fuel pump.
Electrical power is REQUIRED at all times for the Fuel pumps to operate, 
In the event of a VPX or Panel Electrical Bus meltdown, The master switch and any/all other switches including the INT ALT Switch could be turned OFF to extinguish the smoking panel and the Fuel Pumps would still remain powered.
The 5 amp fuse would supply the fuel pump power.
The Diode shown just below the 5A fuse is there to prevent power from back-feeding into the VPX.
- - -
I will assume the fuel pump power circuit continues on to a fuel pump relay, as a 5A Fuse would be too small to power the pumps directly.

Hmm, I think that 5A fuse does go directly to the main pump (not the Aux pump though).  Though it is sharing the load with the VPX.  But, if the VPX fails, then I do think there would be a problem with that fuse.  Up it to 10A?

Fuses are rated to match the wiring, not the load.
If you truly have an 18AWG wire to the pump as shown, then a 10A fuse will be fine.
If your 18AWG wire is rated at 75°C then a 15A fuse is a possibility.