Sounds like a combination of bad wiring/grounds and bad mechanics.

Before you get rid of your car, ask yourself why you would say it is a nightmare. If it is a nightmare because you have discovered a lot of weak points/problems and fixed them, then why pass on a fixed car to somebody else to enjoy the fruits of your labor and cash? With 240s especially, if you keep your eyes peeled as to the condition of the vehicle and do all of the brickboard-recommended maintenance, past problems are in no way an indicator of future problems. When you have a car that will last 400K or more if you treat it right, there are going to be some frustrating years here and there where you end up doing a rash of repairs, followed by lots of trouble-free miles. It's sort of like a marriage that way, isn't it?

On the other hand, if the car is totally lousy and you should not have bought it in the first place, maybe it's time to consider a divorce.

In any case, however, I am of the opinion that nobody should be buying a car with over 100K miles on it that isn't prepared to get under the hood and get a little greasy. Volvo 240s can make excellent daily drivers, but I personally would only recommend them to DIYers. The burden of maintenance is not great, and if you know enough about cars (or are willing to learn) you can recognize or avoid most problems in advance. But if you are of the drive-it-till-something-breaks mindset, I can't think of any 14-year-old vehicle that is going to give you satisfaction, so you might as well drive a Volvo as something else.