Some times only my high beams work. The low beams won't turn on at all. The switch is ok it measures 12 volts when you switch on the head lights but the low beams don't work. I have to drive around with my high's on. But some times it works perfect
Actually you should remove and clean the combination switch headlight portion. You can open the switch up and carefully remove the contacts and polish them. Also do yourself a favor and replace both headlight fuses. New ones will prevent any confusion as to whether or not they have micro-cracks later.
You said the low beams sometimes work so it's not the bulbs...our Z-Cars are notorious for corroded electrical contacts...I suggest tracing EVERY connection from the fuses to the back of the headlights...wiggle 'em with the switch on and if the lights come on (or even flicker) you have found (at least one) poor connection
...it might be a good idea to pull every connection apart & clean the contacts too
...then apply dialectric grease & reassemble...I have an intermittant "high beams
out" and it is VERY frustrating...it is caused by the connection inside the steering column covers from the high-low switch to the headlight harness...someday I will have to replace it...hopefully your search will be a short one!!! )