I have a 1991 740 turbo. Over the past three months, when i turn off the car, the headlights sometimes will stay on with the ignition switch off. In order to make the headlights turn off i have to turn the ignition back and forth a few times, and eventually the lights go off. Sometimes i notice a faint 'click' from inside the dash when the lights actually do go off. With this model, the lights automatically go on when the car is on, and off when the car is off. Another problem - not sure if it's related, is over the last couple days the car will suddenly stall while driving. The engine dies, and all the warning lights on the dash light up. The headlights, and fan and radio all stay on. Sometimes the engine dies briefly, then catches again, before the warning lights all come on, but generally it dies and doesn't restart unless i put the car in neutral or park and restart it. Most times it starts again normally and away i go. When this stalling problem occurs, the tach goes instantly to zero...and doesn't track the actual rpms of the engine as the car is slowing down. It may stall like this ten times in a 15 minute drive one day, and not stall even once the next day. Electrical problem - as in ignition system specifically? Two hours ago i had the electrical portion of the ignition switch replaced. After replacement, while testing the car at the garage, the car stalled a few more times for the mechanic...thereby proving that a new ignition switch wasn't the cause of the stalling problem...at least i thought the headlight dilema would be solved. No luck..when i got home from the garage, (with a few stalls on the way home for good measure)...the damn headlights stayed on when i turned off the ignition! I'm bewildered to say the least. The mechanic who looked at it this afternoon was trying to get me to change the sparkplugs and the fuel filter, as well as the fuel pump relay. We tried putting in another fuel pump relay and the thing still stalled every few minutes. I told him to pack up his wrenches and get outta my hood cause he didn't have a clue, was my response warranted?....anybody here have a clue as to what this may be? Any help greatly appreciated. I love this car, but I hate these mysterious electical volvoisms that seem so commonplace.
Sledge hammer in hand in Ontario Canada.

I'm no expert but maybe my thoughts will provoke a real expert to give you the right answer. First, I would not have thought the switch would be part of the headlight problem ; I would think headlight relay perhaps (I assume there is one - like I say I'm no expert). You can do that yourself. I bit of warning : my opinions are a bit slanted towards things I can fix! First, I wouldn't think of plugs as killing the engine, unless we were witnessing a real sad group of plugs that were limping along in a hard-to-imagine fashion. Wouldn't an intermittent bad coil create a sudden death scenario? Or for that matter just a weird loose wire to the coil. I had intermittent problem when the wire that comes out of the distributor from the sender was grounding out, after a mechanic fooled around with it. Check to see how much corrosion has eaten your wires to the coil, since that's cheap to do. I think it uses those horrible tabs that wiggle free and allow dirt and grime to get in there. Your mechanic thought fuel pump - maybe with good reason. You can get a little tube or a stethascope and hear it running or not. That's cheap. Even a Christmas paper cardboard tube would work fine. Anyway, I think the answer to this depends in part on how many components are reasonably thought to be working bacause of regular maintenance. Was the mechanic putting in plugs because the car was in bad need of them so he might as well start there? Or was it just a blunder? My guess is that it is probably not a fuel problem because the problem vanishes for a day then appears 10 times in 15 minutes. That sounds electrical to me. And despite what I said about wiring, it really sounds like an ignition component failing. Sender, coil, etc. One caveat though, if it dies with a sputter I *would* think fuel control but if dies quick as lightnning I would think ignition. If it were my car I would probably just start replacing cheap parts that were pretty old (electrical parts) until the problem went away since I would figure at the end of the process I would have nice new components.(Plugs, wires, coil, sender, cap , rotor, etc.). Then I would think about the fuel control system. But as I said, this approach is biased towards thing I am able to fix! Anyway I would be happy to hear how one of the experts here would approach it. If I had to guess one thing I would guess impulse sender.