I have a 13plate vw polo 1.2tdi, my headlights and rear lights  don't work but all other lights do. Bulbs have been changed new switch put in and all fuses checked. Any ideas on what may be causing this,, cheers. 

Welcome to the Forum.

 

It might be worth checking that there are good earth connections to the lamps.

 

If you haven't got one, I would recommend that you buy yourself  a basic multimeter, it doesn't need to be an expensive one. I would also suggest that you make up for yourself, a test lamp - nothing more than a bulb on the end of two lengths of wire, a 5Watt bulb would be ideal.

 

The reason for the test light AND the multimeter, is due to the fact that you can go looking for 'lost' voltages with the simple test light, but it is possible that, due to high resistance in the circuit, the bulb may not light (or lights but is very dim)

On the other hand, you can locate a voltage with the multimeter, but due to the high resistance, there isn't sufficient current flowing to light the bulb.

 

 The method then is (1) Locate the voltage with the meter, (2) Check with the test light that there is sufficient current flowing to light the test light.

 

An indication of a poor earth connection MIGHT be that when you switch on say the drivers side direction indicator, other lights at the rear of the car including the opposite indicator also light up (possibly  dimly)

 

Regards