I need to take a step back...
Basic question time.
A "Shunt" is a device placed into a circuit with a known small resistance so that voltage drop across this device may be measured?
It may also operate as a fuse if overloaded, though that is not its primary function.
While many functions of shunts have been taken over by the VPX system and it's not strictly required, a shunt may still be installed if desired.
If a shunt is installed in an electrical system otherwise controlled by a VPX, that reading will be given special prominence in EFIS displays which may make it easier to monitor than the other electrical displays already in the VPX.
If, after taking all of this into consideration, a shunt is desired in a VPX system, the recommendation is to install it in position "A" as shown on page 32 of the Aircraft Wiring Guide.
Close?