[OZ4]

Back to the open ground issue at the volume pot. I must confess there is a ground connection from the low side of the pot to the shaft/mounting portion.

Now my excuses. There is no evidence a external connection. And the carbon track appears to have burned out, its open. So the radio underside wiring was open. Even after removing the back cover of the pot  no connection can be seen. It's hiding underneath the mount.   Rookie mistake  I thought I checked it.