OK, lets sort out the mish-mash of information here:

If a Volvo 240 dies but restarts and the poster of the message gives too little or conflicting information, I always assume it is a fuel pump relay or a fuse related issue. Start with fuses. You cannot inspect the fuses in-place if you are not a Volvo guru...and even then it is questionable. Pull each one out one at a time and check the ends to see if they worn through, check to make sure it is not melted through in the middle. Take a bit of sand paper or a brillo pad to the fuse contacts before replacing the fuse. Rinse and repeat. If your car has the 25-amp engine bay fuse, check that as well.

If you car cranks, turns over or whatever you want to call it (spins but does not start) your primary issue is not your alternator. The car can run for minutes to many hours without an alternator and the battery had enough juice to spin the motor so it is not a lack of electrons.

If it still cranks, spray a bit of starter fluid while cranking. If it starts and immediately dies, your issue is fuel related and has 95% chance of being an intermitently failing fuel pump relay...you can search for "fuel pump relay" on this site and find about a million posts regarding this. Replace or resolder the relay. If you do not trust that assumption, your search will uncover a way to jumper around the relay which allows you to start the car for troubleshoot puposes.

The wire behind the alternator does need to be identified but I doubt it is black. Clean the wire so you can see its true color, report back with the color, what type of connector (spade, ring, bullet) and if it is a thick or thin wire. My guess is that it is either a temp sensor or oil pressure sensor wire (thin) or the alternator ground wire (thick). Non-Volvo mechanics do not realize that the alternator is electrically isolated from the engine by the bushings and often do not connect up the alternator to chasis ground wire. The ring terminal on that wire also fails due to vibration, location and corrosion.

Onkel Udo