A little warmth is the answer. That is why the instrument lights alleviate the condition. An easy solution is to add heat. See below
http://www.oemheaters.com/c-983-freezestop-12v-heat-cable.aspx?gclid=CK-QscjY3KwCFeddTAodOn21-Q

Something of this nature wired to the run position of the ignition

'65 +4 four seater