License plate light drain?
This is a guess on my part, but could it be a vent tube for a rear mounted battery box? My '64 Overlander has a rear mounted battery box with a vent tube that is directed to a small opening near the center rear below the window.
Kevin D. Allen
WBCCI (Lifetime Member)/VAC/Free Wheelers #6359
1964 Overlander International/1999 GMC K2500 Suburban (7400 VORTEC/4.11 Differentials)
1978 Argosy Minuet 6.0 Metre/1975 Cadillac Eldorado Convertible (8.2 Liter V8/2.70 Final Drive)