My son's '79 242GT has a perplexing "quitting" problem that is driving us crazy in diagnosing. Only happens occasionally, but in both hot and cool outside temp conditions. If he is slowing for a stop or turning, the engine dies and usually will not restart. Son claims that when this happens the amp idiot light (only) will come on and stay on afterwards. Sometimes it will finally restart after sitting for several hours, and at other times we have had to tow it to shop (where coincidentally it never fails to start). Seems to be getting fuel but no spark. Thus far we have repaired the primary fuel feed and the other day replaced the original fuel pump relay. Last night it died again. This morning I eventually got it to restart after many cranking attempts. Drove it around a few miles and it was fine. Previous owner mentioned this happened to him occasionally, perhaps when he was using the turn signal, and after R&R'ing the ignition relay fuse it would again start. Also, car has an MSD ignition setup. Any suggestions?

thanks,
bob