factory trailer brake plug voltage

[h500r]

hi
2005 ford f250 v10
found a tech article that says
early 2005 1 to 2 volts + for trailer brakes ?
late 2005 and up 11 to 12 volts + for trailer brakes
does anyone know what changed in mid 2005
to cause this voltage change ?
my friend juat bought a early 2005
and it has 3 volts at the brake pin
cannot get the trailer brakes to grab
his old 1979 and my 2008 diesel has 12 volts at the
pin and the brakes work fine
is there a fix out there for this??
the 2 local ford dealers are clueless
thanks for any help