First, I don't want this to turn into a "why" argument. This question is simply about "how".

I'm plumbing my line-lock to lock OUT the backs. I've seen here from a few people that to do this, you need to plumb the solonoid backwards (in is now out, out is now in). My question is: WHY would you have to do this? Does't the solonoid simply interupt the line? or is there something else going on? is it maybe essentially a one-way valve? I just want to really understand what I'm doing here. Thanks guys.

The Line Lock is a simple electric valve that closes when 12 volts is applied.

Mine is plumbed in the front brake line. I step on the brake pedal, push the button, then release the pedal. Front brakes are locked and rears turn free.

i'd like an answer to this as well. I think it would also give you a poor man's indicator light since the factory light would come on if you pushed the brake and there was no pressure to the back?

No light will come on . I have mine plumbed just as Bill says his is.Hit the pedal, hold the switch button, release the pedal and fronts are locked solid.
Gary.....What brand of line loc do you have? Hirst Roll Control???
Richard

Well, I'm waiting on my 3rd Summit brand solonoid. First two had identical manufacturer defects, fluid flow hole drilled off center of threaded fitting hole.

The guy at summit said he didn't understand why you'd have to plumb it backwards, as it just locks the line. The solonoid shouldn't know which side the pressure is on (???)

Just plumb it into the rear line same as you would do the front, I've done a few like that for parking lot antics- lets you control the speed of the car while doing stupid crap, I wired it on a toggle instead of the momentary push button switch so I didn't have to keep my hand on the button.

I always thought this was because the valve was a one-way valve, which means you could pump the pedal several times to build the pressure up and then lock it in.

By plumbing in backwards you do not lock the pressure in the front system, instead you can still use the front brakes as you apply the brake pedal, ie you control the brake application directly through the pedal and just pushing the pedal in does NOT lock the front brakes.