Right, I got bored of quoting all of the misleading information in the thread, so here is what WILL sort out the "Headlights remain on after switching the ignition and lighting circuits off!" issues.
Quotes from the topic;
It doesn't matter what position you put the switch into, the lights remain on when the ignition is off. Also, after some time the Headlight Control Relay WILL start to buzz as the voltage causes the coil to become temporarily energised. The switch IS NOT at fault!
The relay contacts are NOT welded together, and there is only a single relay which controls the lighting circuits. Taking the relay out will solve the issue temporarily, but this isn't an ideal route!
Misleading information alert:
There is NO ECU controlling the lights. The ECU you would be referring to is the "Theft Deterant ECU" which controls a number of functions on the Lexus IS200, including but not limited to the lights.
Switching to "Auto" and turning the engine off will do nothing to solve the issue.
Cleaning the sensors will do nothing to solve the issue. Removing them from the circuit does nothing to solve the issue.
The RAC bloke was along the right lines. The fault that will have come up on his scanner will be something along the lines of "Headlight ECU Programming Lost". This actually refers to the "Theft Deterant ECU" which will have burnt components inside caused by shorting.
Shut up! The fusebox DOES NOT need replacing, Lexus Derby attempted to do this on a family members car, as they could not diagnose the problem fully. There may be oxidisation on some of the contacts, but this can be cleaned and by no means does it mean a costly replacement is needed!
Because whoever fixed it for you DID NOT address the route of the problem.
So, you're probably wondering how to solve the issue? Well, thats what I've managed to do on a 1999 Lexus IS200 successfully for the last 2 years.
The replacement part you need is the "Theft Deterant ECU" available direcly from Lexus if you wish to pay through the nose, or you could do what most sensible people these days do, and request one from a salvage yard. They regularly come tested and with at least a 3 month warranty on them, you'll know immediately if it's good or not as it will or won't solve the issue.
Further to this, you also need to have the windscreen removed, resealed and reseated properly. RAC, Autoglass and other major Windscreen Replacement Companies ARE aware of the issue with the Lexus IS200 and the front screen heater connections on the bottom drivers side of the screen.