MG Car Repair: Low Beams Quit Working, low beams, high beams

Question
I purchased a 1972 MGB for my wife last year and have been slowly working out all of the little issues with her (the car). We had her out last night and when we went to turn on the headlights the low beams failed to come on. High beams and park lights operate perfectly.Not being very fluent in wiring of reading wiring diagrams the first thing I did this morning was replace the aftermarket headlight switch the previous owner had installed. No difference, still no low beams. Any and all suggestions would be appreciated.

Answer
Hi Ken,
The dimmer switch needs to be tested for power to the low beams when the dimmer switch is flipped to low beams. Check the blue w/white and the blue w/red tracer wires at the plug connector for the dimmer switch as you dim the headlights. If that is ok proceed up to the headlight bulbs for the same tests.
Howard