Voltmeter low reading issue

john leblanc said
with headlights and vent fan on high dash amp Gage shows charging,

It seems like your gage is hooked up backwards.

john leblanc said
both voltmeters drop to 10.5 volts, what gives???

Almost certainly the wires on the gage are backwards (or the wiring has been modified)

john leblanc said
Amp meter in dash showing good charge

Well its possible the battery is not fully charged because if it showing charge on the ammeter, then the battery is still sucking current.

john leblanc said
maximum charge on battery 13.2,

The only way a battery post will be at 13.2 volts on its own is just after being charged, there is a 'surface charge'.
but tell us
Was this voltage reading made when the engine was running and the meter showing charge?

john leblanc said
under dash voltmeter max read 11.5 volts

What is that meter connected to?