The non synchronous vibrator type used in the 47-53 gmc and Chevy truck radios in the USA do not care about polarity
Your radio can swap between ground types.
The synchronous vibrator used in the Autoradio model 490 for for 47-49 trucks in Canada does care about polarity and there is a warning label indication to swap the rotation of the vibrator according to the ground type
Later Autoradio changed their circuit to the non synchronous style by the model 510 and added an 0Z4 so the 1951 and later radio could interchange without that detail. I forget off hand the model 500 was between those two.
Source: I have all these radios in my collection and original documentation.
-s
