With the engine off, I flick the sidelights on and they come on fine without the main lights popping up. With the car running, the main lights pop up when I only want my sidelights on. How do I cure this?You need to remove thedim diprelay. It is located on the passenger side of the engine bay under a black plastic cover. It should be nearest the wing and firewall. Unplug it and this will stop the barn doors opening on sidelights. Take the black cover off and you will see a few relays, the one you want should be on the right nearest the firewall. Mine was marked HD22. You may find it easier to remove it from the metal bar (prise with a screwdriver) to unplug it as it can be a pain. Should take no longer than five mins to do. Here’s the bay, right and slightly down of the wiper motor you can see a black oblong , that’s the cover the relay is under.On Mk1’s with ABS there are actually what look like five relays on the mounting plate under a black cover. Three in front you can see and two hidden at the back against the inner wing which I couldn’t see at first. It was damn near impossible to get to the rear relays without unbolting the relay mounting plate…a bit fiddly but possible if you are lucky enough to have sockets of the right length to work around the ABS unit and the wiper motor. In common with other 5’s you then disconnect the relay marked HD22 which interestingly was the one furthest away from the bulhead…not the closest as normally seems to be the case. Now no dim dip. Great!