Main dipped headlights not working

I think dipped is UK speak for not the high beams
GJUK, Take a look here,
http://www.mymopar.com/downloads/1968/68DartA.jpg
http://www.mymopar.com/downloads/1968/68DartB.jpg

Buklhead wiring connector at firewall is a known problem spot.
Then I would look at the Hi/Lo footswitch.