I spent some time on this today and have ruled out the switch as I have tried the switch from my other '73, and the problem persists.
When I switch the lights on, it seems that they are permanently on bright. When I use the dim/bright switch, the blue light on the dash comes on and off like it should, but there is no difference in the actual Beam. My car is a UK spec car, so has a flash button on the stalk as well. With the lights off, if I depress the flash button the brights come on as does the blue light on the dash. In this instance, I can hear a relay making the switch.
In normal operation though, even though the blue light on the dash comes on, there is no sound from the relay. The relay looks standard as it is wired into the original harness on the passenger side kick panel with a multiplug. Very confusing.
I'm thinking this is definitely a wiring issue and not the switch. I'm going to trace the wires from the relay to headlights tomorrow and will hopefully see something blatantly wrong :-). Any advice is very welcome......
Edited by Classicman, 17 March 2016 - 06:01 PM.