[s-cars] EDL fill me in

[Steve Voit]

Can someone explain exactly what the EDL does or purports to do? Which diff?
Lock under what conditions?  How?

Why is it the later cars don't have a switch?

I'm having differential 'binding' and 'gear tooth rumble' (slow speeds
parking lot radius turns, accelerating during stop sign turn) through seat
of pants; this in a new to me 6-sp EDU tranny.  Could it be EDL doing or not
doing what it's supposed to do?

Thanks guys,

Steve V.