What does the Lock-Up Relay Do?

There is a wire that runs from the lockup relay to a vacuum switch then back to the ecu. What function does this server the ecu?

And where the hell is it? I've been looking for threee days.

 

If you have an auto tranny it's the tourque converter lock-up switch. Basicly it's like fully releaseing the clutch on a manual trannied car.

 

I'm finishing up a auto to man swap.

Can I just leave it alone?