That script was for turning lamp-posts on and off. Not the same as vehicle lights. For a "logic" that you've put in the driver seat of "humvee":
while {true} do
{
logic setBehaviour "safe"; // Lights won't stay on unless "safe" or "careless"
humvee action ["LIGHTON", humvee];
sleep 1;
logic setBehavior "combat"; // Lights won't stay off if "safe" or "careless"
humvee action ["LIGHTOFF", humvee];
sleep 1;
};
Try searching for "LIGHTON" and "LIGHTOFF" (I know, searching never helps unless you know what exactly to search for) and there seem to be several discussions about lights, but not specifically about flickering.