Triumph Repair: TR-4A headlights, voltage stabilizer, high beams

Question
I replaced my voltage stabilizer in the passenger foot-well last weekend when my temperature gauge started reading way to hot for reality.  The replacement corrected the gauge problem but now both my headlights work only on high beam.  I get no illumination at all on low beam though the blinkers and running lights all work just fine.  I replaced one of the lights as a test and still got only high beams.
Both fuses in the engine campartment appear to be in good order. Is there a headlight fuse elsewhere? Can you suggest what might have happened and how I might solve this problem?

Answer
Hi Tom,
You need a wiring diagram to work on any part of the electrical system and a 12v test light and just start tracing from load (in this case the low beam) to the switch going from one connection at a time and you will have to find the loss of power. The "Hunt and Peck" method is a large waste of time and energy. If you don't have a diagram let me know and I will put one up on my web site for you to copy.
Let me know,
Howard