New to this site but need help with an electrical fault on my Series 3. Indicators and horn work ok when i start the Landy but when i switch on the lights they stop working, the main beam doesnt work and the sidelights and indicators come on!!! This was intermittant but now the fault is permanent. Any bright ideas would be appreciated. I found that if i pressed the horn a few times everything would start working normally but now this does not fix the problem.

Welcome. A common S3 problem. Take this to the series section and you'll get advice. It a short in the circuit. Check the fuse box partularly the seating of the fuses in the holders. Take off the front grill and check all the connections lying in front of the radiator - they can get loose. Check the connections behind the headlamp holder in the wheel arch lots of crud corrodes the connections and wiring. Also check the connections on the loom in front of the battery and if there are relays fitted check the connections. There's a fault somewhere in there.