Hello James and thank you for your reply. Searching the topic here at Brickboard I came across the bulb holder issue at (white on the passenger side, black on the driver side), but that is the way the bulb holders have been in the car all along. Still, I seem to remember that may years ago I damaged one bulb holder (white, I think) and was sold another one from Volvo but black at a local European auto parts store. I doubt it is possible to mix up the circit boards (films) because of the way they are made and folded where the wire harness connects. Today, I cleaned those circuit boards first with a soft emery board used for buffing fingernails, and then with CRC electronic contact cleaner spray, before I coated contact surfaces with dialectic grease to keep them clean. Then, I put in a pair of brand new 12V Osram P21/5W bulbs with the BAY15d base. This is the OEM type of bulb specified in the owner's manual, but is it any different from 1157 bulbs? I checked that only the 5W filaments are on with parking lights on and the 21W filaments come on only when the brake spedal is depressed, both right and left sides. The lights have worked well all day today, but those lenses are likely melting again, even after I heated them and shaped them back as best I could today. Please, give me your suggestions to trace that short, as it is the only avenue I have left now. The other possibility that comes to mind is bad quality of the tail lights I bought from Frank's Auto Parts (New and Used Volvo Parts), but they refused to help. Best regards.