Mazda 626 Low-beam lights won't work - HELP please
 

The low-beam head lights on my Mazda 626 (1990) has just stopped
working!
I have checked all the fuses - all OK.
When I switch the lights control-lever to high-beam, all 4 head lights
come on, and yet if I switch it back to low-beam, all 4 lights will go
off.
Does this mean that the 'control unit' at the steering is defective and
needs replacing?
If this is the case, do I have to replace the whole unit, or can I just
replace faulty switch at the base of the lever?
Many thanks in advance for your advice.
-Mike