There is a dimmer switch, it is hidden right under the dash. Serrated wheel with axis from door to door about the size of a new 10p.

Sit in the drivers seat and place your right hand on the dash just next to the wheel column. Slide your open palm down and just feel around for the wheel.

Or stick your head under the dash and take a torch!

Everyone loves a Morgan. Even me, unless it's broken again.