RE: 91 s10 stalls when lights are turned on
Can you tell if the DRL relay is still energized after you turn on the headlamp switch? It shouldn't be. You might unplug the DRL relay, then see if the headlamps still work? They may not, some of my info shows, when the DRL relay is not energized, the switch side of the relay acts as a ground for the headlamp.
Does the battery have a good charge, are the cables clean on both ends, does the charging system work ok? Are there any codes?
Are you saying, when the problem happens, andthe vehicle dies, it cranks good but won't start?