When I switch on my side lights heat rear screen switch illuminates and no headlights

You don't say which model but guess from avatar 300tdi. Think rear screen switch should light with side's
You do have ignition on ?

Yes it a 300tdi all started with heater suddenly stopped working on investigation position 1 on the key had no connections at all & according to heater wiring should be feeding from this position to fuse 5 on a with a white orange wire , located this wire coming off my running lights which had blown a fuse = y heater had stopped working, re-routed white orange on to position one on ignition, ( the dipped headlights not working was me been a knob as they don't work on position 1 on ignition der)