I don't really know for sure, but since no one else has answered, I'll give this a shot. You said the switch was new, so someone had to have installed it recently. So since it does work (somewhat) and it works fine going the other way, I would say check the wiring and the connection. Maybe upon installation of the new switch something was not connected as well as it should have been.
'86 420SE Euro
904 Midnight Blue, Gray Velour
Dad bought it new, now I own it.
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