Hey there,
Well I will add my 2 cents here as others will I am sure.
The button on the old VW type turn switch was used to activate a hi /low switching relay in a VW same as a lot of new cars. So if you want to go that route it should be easy to find a relay.
However I believe in the Cobra it is used as the horn switch and the foot operated hi /low headlight switch is mounted on a bracket to the left of the clutch pedal also how it was done in many older cars.
As for the heater valve it is a manually operated tap / valve on the intake manifold where the heater hose attaches and the switch on the dash really only does control the fan.
I am building an early 289 style roadster and have been sourcing most of my Lucas style knobs and switches from moss motors.
The latter 289s had off the shelf 60's Ford stuff and then the 427's went back to the British stuff. So if you want it "correct" Moss motors might be the answer for you too.
Just my 2 cents
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Yes, I know,....... but it's mine you see.....
Perhaps he was always a shyster, but we just chose to over look it for awhile.
You build what you like and I will build what I like...it's all good
You know that guy,
The one in the neighborhood who likes to hang around the garage while you are working and talk about back when he had that killer 1977 Chevy Mustang