Jon,
Mine's an S130/5 from November '72 too ! Don't you just love the simpler SINGLE fuse box wiring ?! This was one of my requirements when I was looking to buy a car...
It's in the Workshop Manual on the +2S130 wiring diagrams (Federal & non-Federal) - look for the little switch just above the 'triangular' Dip Switch. It is shown as a switched brown wire from the feed side of the Lamps Switch to the Main Beam (blue/white wires) 'terminal' on the Dip Switch.
When I last dismantled the Dip Switch (!), I looked at the headlamp flasher arrangement too. The wire on the flasher part of the switch had broken off, so I reconnected it - still no flashing headlamps !
Aha! I've just noticed from the wiring diagram that the only way the headlamps can flash AND be in the 'up' position is if the Dip Switch is in the Main Beam position. Perhaps I will try that tomorrow !! Thanks for the 'inspiration'
Has anyone out there got a headlamp flash that works ? If so, is it any good ?
Best wishes,
Matthew