You might check the alternator belt tension. I had a situation once on our old 144 where the belt became loose just to the point that it would turn the alternator enough to keep the idiot light off but not generating enough current to support headlights, heater blower, fuel injection pump, etc., etc. The car would run if I turned off the headlights and heater fan so, since it was night time, I tailgated the car in front of me all the way to the next funky little gas station. Noticed the belt was a bit loose so I snugged it up and that brought the electrical system back to normal.

Also, don't the 240's have some high current wiring running underneath the crank pulley that sometimes gets oil soaked, causing deteriorization and shorting? It recall discussions here on the BB about that issue.